newbie's question about ap using camera lens

[carbonplay]

i am considering to start my astrophotography and will highly appreciate your advice.
i have a sigma 300-800mm f/5.6 lens. i think it gonna be a good refractor considering its aperture is almost 6''. Is there any difference by using this lens compared with a telescope?
my second question is how i can auto guide using camera lens. since camera lens does not have dovetail plate on top and there is no way to attach second guide scope, i am very interested in finding how other people address this problem.
Thanks!!!

[Catanonia]

Hi there, being a newbie is great :) I am only about 3 weeks in and have gone completely over board.

The 300 - 800 will work, I have a 170 - 500.

Although it will not give you as good as pictures as a telescope, it will get you going.

As for tracking. Try this web page

http://www.modernastronomy.com/mounts.htm#maAzimuthBolts

And look at the AstroTrac that fits on a ball tripod for your camera. Really clever engineering, but a tad expensive.

I got into this really quickly and ended up spending £2000 today to get proper equipment. It is really addictive especially when you get your 1st images.

I suggest trying to set the zoom to 300 and stacking quite a few 2 second exposures together. Any more than 2 seconds and you will, like I did, get star trails on that size zoom. The F6 is good, but are you sure it is that at 800mm ? Don't know my lenses that welll.

As for autoguiding with camera, you should be able to if it has live view and the guiding software can see it. Whether it will be able to pick out faint stars to guide on is another question. If you really want to go into autoguiding, then really you need an EQ mount and guide ports / software to move the camera. The AstroTrac will guide in a linear motion as long as your polar alignment with the polar scope is bang on.


Good luck dude

[Bill Boehme]

That is one big lens. Vibration will be especially critical with such a long FL so you will need a very solid telescope mount. Most photography tripods are not solid enough.

You need to attach an Arca-Swiss style double dovetail plate to the mounting foot of the lens. Wimberly makes a very good one.

With such a long FL, shutter vibration will be a big problem on short exposures such as the moon. You could try "hat trick" exposures for moon shots. You will not be able to do long exposures unless you either piggyback on a telescope or get a telescope mount and drive for the camera and lens. Manual guiding can cause you to become demented. ;)

[carbonplay]

thanks for all your kind reply.

i did some research for equatorial mount today, seems like Orion Atlas EQ-G will be my next investment. but for EQ mount, they normally use vixen or losmandy type mounting plate. can you share some experience with these mount types? how compatible with arca-swiss mount?

thanks!

[Bill Boehme]

thanks for all your kind reply.

i did some research for equatorial mount today, seems like Orion Atlas EQ-G will be my next investment. but for EQ mount, they normally use vixen or losmandy type mounting plate. can you share some experience with these mount types? how compatible with arca-swiss mount?

thanks!

I suspect that they might not be compatible even though similar in appearance since the Arca-Swiss is intended for attaching a camera or lens to a quick release bracket on a tripod ball head. The Losmandy and Vixen plates are probably larger. You could contact Wimberly (www.tripodhead.com (http://www.tripodhead.com)) for more information. I have found them to be very helpful.

[chris.bailey]

Your Bigma will be an OKish refractor for Astro use. Dont expect good colour correction and field flatness though as these are less crucial in ground based photography.Expect odd shaped blue tinged stars at the corners of the field. Expect getting it into focus to be a major PITA!

[Peerie]

Unless you are in love with your Bigma, why not sell it and buy an astro setup and then use the rest to buy a 500mm lens.

Must start with the mount, must be solid. Why not look in the classifieds section of either Cloudy Nights (mainly USA sales) or Stargazer's Lounge (mainly UK sales). Could save a significant amount of money going down this route.

John

[carbonplay]

Thanks for your advice. But i do love my sigmonster. it's a perfect tool for shooting birds.

someone in FM actually said 300-800mm was comparable to Takahashi. since there are full of expert in this forum, i think it's better to gather some first hand advice here.

BTW: I think bigma is referred to 50-500mm? am i wrong?

[chris.bailey]

Comparing a Bigma to a Tak scope is like comparing crispy aromatic duck to a crispy creme doughnet. Both good in their own way but toally different. Big primes come closer but the optics are designed for totally different purposes. I tried my 100-400L for astro and its not in the same continent as my Tak FSQ but I also would not want to take my Tak birding.