My iOptron

I just recently purchased an iOptron Sky Tracker, and finally got clear skies to try it out. Roy A. Rust has been giving me a lot of tips, which I greatly appreciate.

I used my Sigma 17-70 lens on my 60D. One thing Roy told me was very important, was to use Live View zoomed in for focusing, however when I tried using Live View I could not see squat on my LCD screen either at 17MM or at 70mm, and zoomed in on Live View. So I put the infinity mark at the focus mark, and what I can see the images looks pretty good. Perhaps some one else here will see something I do not.

The first image I was pointing towards Jupiter. I have no idea why Jupiter has a line going straight down. Does anyone here have any ideas what caused that? The second image pointing towards the Little Dipper. Each image taken at 60 seconds 17MM f3.5, and each image I cropped the center at 100%

I have a lot to learn yet, so please be gentle with me! Please critique these images.

Towards Jupiter

IMAGE LINK: https://flic.kr/p/GJBR​bM

IMAGE LINK: https://flic.kr/p/HEcc​uF

IMAGE LINK: https://flic.kr/p/HEcc​9a

IMAGE LINK: https://flic.kr/p/HBg8​Hd

Red/green/blue dots are hot pixels, zoom in on pixel level and they will be square.

Don't forget to mirror your Polaris alignment based on the location you find in an app, so if Polaris is at 6 o'clock in your app you put Polaris at 12 o'clock in your scope.

pdxbenedetti wrote in post #18023345
Red/green/blue dots are hot pixels, zoom in on pixel level and they will be square.

Thank you

What causes the hot pixels?

pdxbenedetti wrote in post #18023345
Don't forget to mirror your Polaris alignment based on the location you find in an app, so if Polaris is at 6 o'clock in your app you put Polaris at 12 o'clock in your scope.

Yes I did that best I could. As I was looking thru the reticle, just moving my head around I noticed Polaris was moving a lot more than I did. I did not understand that either.....

Thank you again

Sorry, I should clarify, colored pixels (Red, Green, Blue) are usually stuck pixels and will be present in the same location in every picture you take, but they come and go (I've read varrying ways to "fix" them, but it's a problem most sensors have at some point or another). Hot pixels are the result of thermal noise, the sensor getting hot while taking long exposures, and are generally seen as white spots throughout an image (obviously not stars in terms of astrophotography). Every sensor will have it's own thermal properties and develop hot pixels differently, not much you can do about it with a DSLR, astrophotographers with CCD cameras on telescopes can cool their sensor.

In terms of Polaris "moving" around as you look in the scope, you need to look through the scope in a stable position. I find that the polar scope on the iOptron doesn't have great optics and imperfections in the glass lead to stars appearing to move depending on the angle you look through. Try to stabilize yourself, sitting upright and keep your line of sight straight through the middle. If you start to angle yourself to get a different position or the scope is angled downwards/upwards/side​ways polaris will appear in a slightly off position. Achieving a good polar alignment will mean that Polaris will travel around the circle counter-clockwise throughout the night and not drift inside/outside of it. I've gotten good enough at doing the polar alignment where this is regular for me. Another important thing to do is making sure your tripod is very level, if it's not level polaris will drift substantially out of alignment over time. I can get 15 minute exposures with a wide angle lens on the Skytracker these days.

I'm not sure if you've read through this thread, but there are a lot of good suggestions in here with regards to the Skytracker:

(I'm going to link to the last page since it's the most recent and people have had the most time using the Skytracker)

https://photography-on-the.net …ead.php?t=13648​49&page=21

In terms of your exposures, you need to increase the ISO to 800 or so, no need to go higher than that with the Skytracker. Your aperture is fine, I'd try and increase your exposures to 2 minutes or so and see if you get any star trailing.

Thank you. I have read most of the thread you mentioned to me. I did do (2) 2 minute exposures last night. Here they are.....

IMAGE LINK: https://flic.kr/p/GJXK​1w

IMAGE LINK: https://flic.kr/p/Hyp5​dK

Your 60D does "exposure preview" when in live-view mode. I have a 60Da (identical camera ... just a different internal filter to allow more Ha light to pass). To focus it, put the mode dial in Manual (which you're probably using anyway -- no other mode makes sense for astrophotography), crank the ISO to the max, crank the exposure time up to 30 seconds. The the aperture to minimum (whatever wide-open is for you lens).

A photo taken with these settings would be overexposed and you'd probably have a muddy sky, but it causes the camera to amplify the image of the stars for purposes of focus during live preview.

Find a star and zoom in to 10x on the live-view (you can use the 8-way navigator to move the zoomed area around the screen). Once you're satisfied that you have good focus you can return to better exposure settings.

A 60D tends to do well at ISO 800 (each camera is different but I find this works well for the 60D/60Da).

You can get focusing aids. Astrojargon.net has an online tool that will let you generate your own Bahtinov focusing mask (you print it out, trace it to something more durable, and then cut out the slots). You can also get commercially made focusing masks. The mask through a diffraction spikes (hint: needs a bright star -- don't use a planet, use a star. You can also take a test exposure and the diffraction spikes are more visible in longer exposures.). When the diffraction spikes all converge at a common center point then you've nailed the focus (then carefully remove the mask without bumping the focus ring and you're ready to shoot.)

Picked up one of these at Amazon several weeks ago for $250.

Nice well built unit, portable, great product, but then there is the battery compartment. A purely embarrassing piece of engineering.

There is another thread here where some have chimed in with some DIY mods to get that not be as much of an issue. I'll be headed there soon to read, thanks to those in advance for sharing their fixes.

I did buy a Star Adventurer last week, but I haven't used that for really long exposures, the iOptron Skytracker is the one I've done 15 minute exposures on. This one is 12.5 minutes if I remember correctly and not even with a good polar alignment, just Polaris in the rough area of the circle of where it was supposed to be:

http://i.imgur.com/hdF​trgY.jpg

Clouds were out so I was just messing around with really long exposures, that's why the stars are all blobby. There is a little bit of star trailing, but I chalk that up to the alignment not being perfect.

TCampbell wrote in post #18023601
Your 60D does "exposure preview" when in live-view mode. I have a 60Da (identical camera ... just a different internal filter to allow more Ha light to pass). To focus it, put the mode dial in Manual (which you're probably using anyway -- no other mode makes sense for astrophotography)

It does make sense to me. In Manual I found I could not go longer than the 30 seconds. I was in Bulb Mode so I could go as long as I wanted, which when I took these pictures I went to 2 minutes.

TCampbell wrote in post #18023601
, crank the ISO to the max, crank the exposure time up to 30 seconds. The the aperture to minimum (whatever wide-open is for you lens).

A photo taken with these settings would be overexposed and you'd probably have a muddy sky, but it causes the camera to amplify the image of the stars for purposes of focus during live preview.

Thank you. Now this sounds like a good reason to use Manual mode.

TCampbell wrote in post #18023601
Find a star and zoom in to 10x on the live-view (you can use the 8-way navigator to move the zoomed area around the screen). Once you're satisfied that you have good focus you can return to better exposure settings.

A 60D tends to do well at ISO 800 (each camera is different but I find this works well for the 60D/60Da).

You can get focusing aids. Astrojargon.net has an online tool that will let you generate your own Bahtinov focusing mask (you print it out, trace it to something more durable, and then cut out the slots). You can also get commercially made focusing masks. The mask through a diffraction spikes (hint: needs a bright star -- don't use a planet, use a star. You can also take a test exposure and the diffraction spikes are more visible in longer exposures.). When the diffraction spikes all converge at a common center point then you've nailed the focus (then carefully remove the mask without bumping the focus ring and you're ready to shoot.)

I went to Astrojargon.net and found the Bahtinov Mask Generator. Looking at it, I see it was made for telescopes which I do not have, and I have no idea how to convert the numbers to make it work for my lens, but I guessed at:

Focal Length 500
Aperture 5
Edge Thickness 15 (left this where it was)

This is what it gave me:

What does 'Edge Thickness' refer too?

I see that will work just fine!!! JK

I was hoping the sky would be clear again Sunday night... and it was!!

Well, looking straight up and to the south it was very clear!

Looking straight up and to the north not so much. I could sorta kinda see Ursa Major. I could not see Polaris at all.

Bummer

I've done a "blind" alignment before, as long as you don't adjust the Skytracker from a previous night when it was aligned if you have a compass you can get Polaris in the general area (and a level tripod). I've found that's good enough for me to get at least 1 minute (and maybe longer, I didn't push it past that) exposures with no star trailing and a wide angle lens (24mm). I put the compass flat (level) above the polar scope and pointed it north.

pdxbenedetti wrote in post #18024459
I've done a "blind" alignment before, as long as you don't adjust the Skytracker from a previous night when it was aligned if you have a compass you can get Polaris in the general area (and a level tripod). I've found that's good enough for me to get at least 1 minute (and maybe longer, I didn't push it past that) exposures with no star trailing and a wide angle lens (24mm). I put the compass flat (level) above the polar scope and pointed it north.

That sounds like a fairly good idea. The ground I was on Saturday night I guess is somewhat level. I have a 'cheap' compass but would like to get a better one someday at a sporting goods store, or at least find something there then see if I can find the same one cheaper online.

Hmm... I tested AstroJargon and wasn't having a problem. I'm wondering if you inadvertently changed something else. If you'd rather get a commercial focusing mask, here are a few options:

1) Gerd Neumann makes masks which screw onto the front of your lens just like a normal filter. They come in various filter thread diameters (just like normal filters) so you'd pick out the size for the lens you plan to use. This makes it a little less "universal". The downside is that they are rather expensive (I see the 77mm diameter mask priced at $109 USD). They are very well made -- not plastic. It seems to be machined out of metal which is then treated to make it flat black.

2) A MUCH more affordable option is the Farpoint "unmounted" Bahtinov focusing masks. It's "unmounted" because it's designed to fit on an existing camera filter (e.g. if you already have a clear filter or UV filter for your lens, you can buy this, it fits into the threads on the front of your filter and then you attach the filter to the camera lens. I'm checking OPTcorp.com and I see this mask (designed to fit into a 77mm diameter filter) is priced at $11.80 USD. But it is a little less "universal" in that they also come in sizes (to fit into your clear filter) which means you'd need to decide which lens you plan to use most often (of course at less than $12 you could probably afford to get a few of them for any lens you think you might want to use.)

3) A bit more "universal" is the SharpStar2 focusing mask by Lonely Speck (lonelyspeck.com). This mask slides into a filter holder such as a Lee filters holder or a Cokin filter holder. These are "square" filters that slide-in to the filter holder slots. Lee Filters makes holders in three sizes... 75mm, 100mm, and 150mm. Cokin makes filter holders in 67mm, 84mm, 100mm, and 130mm wide slots. 67mm is really intended for use with point & shoot cameras. The 84 and 100mm sizes are designed for use with DSLR cameras (with 100mm being the most common AND it's the one size which is common between both Cokin and Lee Filter systems.) The holders on both systems require that you get an adapter ring (they're cheap) designed to fit the thread diameter of your lens (it snaps into the filter holder so that the filter holder will mount to your lens.) I bought the 100mm width SharpStar2 and it slides in my Lee filter holder. Due to the way it mounts, I could attach it to any lens that has filter threads on the front (the most I'd have to do is buy another adapter ring -- but those are cheap.) The price wasn't bad... $69 USD for the 100mm size. Incidentally, this filter is "clear" (unless most Bahtinov masks which are solid black with clear "slots" cut into them) and it's etched to throw the diffraction spikes. The upside of this is that more light is passed (a typical Bahtinov mask probably blocks about half the light -- so you really do need a bright star to focus.)

As with all Bahtinov focusing masks, you need a bright star and it must be a star (not a planet) -- don't attempt to use it to focus on, say Jupiter for example. The diffraction spikes won't be tight if you do that and it will be difficult to see if the spikes converge at a common center point. But the good news with focusing objects in space is that if ANY object is focused, then EVERY object is focused. So pick any bright star, focus, and then re-point the camera to the section of the sky you want to image.

I was never _really_ able to achieve good focus until I started using a focusing mask. I always just got pretty close, but could tell the stars were all just a touch soft.

TCampbell wrote in post #18024797
Hmm... I tested AstroJargon and wasn't having a problem.

This is what I changed:
I changed nothing below in the advanced parameters...should I have?

What does Edge Thickness refer to?

Inspeqtor wrote in post #18024888
This is what I changed:
I changed nothing below in the advanced parameters...should I have?

What does Edge Thickness refer to?

Hosted photo: posted by Inspeqtor in
./showthread.php?p=180​24888&i=i21112755
forum: Astronomy & Celestial

Ahh! It's the "5" that's the problem.

They really want to know what the physical diameter is of your objective lens (don't think of this like an f-stop value). If I look at the tech-specs on your lens (http://www.sigmaphoto.​com …00mm-f5-6-3-apo-dg-os-hsm) it looks like it's roughly a 95mm diameter at the front. The filter size is 86mm. That means the lens body is about 9mm wider than the objective lens (or another way to think about it is you have roughly a 4.5mm border around the objective lens).

So the values you would enter are:

focal length: 500
aperture: 86mm
edge thickness: 5mm (I rounded up from 4.5mm)

Try entering those values and I think you'll find you get something much more useful.

You can then print it out, transfer it to something more durable, and use a craft knife to cut out the slots.

Once you get the idea of how this works, you could make one just a tiny bit smaller to fit "inside" the threads of a UV filter... or you could put some tabs on the outer edge to allow you to fold it back and secure it to the front of your lens (perhaps with a rubber-band). Just be careful with removing it from your lens so you don't end up changing the focus (it looks like the focus ring is not right up against the front of that lens so you're probably fine.)

When I use the parameters above, I get this: