Beginning Astrophotography

jermng · Post by **jermng** » Mon Sep 10, 2007 2:15 am

Hi all,

I was just curious what local astro-photographers would recommend in a beginners setup for astrophotography. With the local prices and shipping differences, the local astro market seems to be quite different from that in the US.

I'm currently using a C8 and an 80mm f/6 widefield scope so I think scope wise I'm ok, but my mount - an Orion SVP has not been performing very well (visually ok, but photography is really pushing it when I tried to use a DSLR w e 80mm)

What would be a good mount to consider and what CCD camera is recommended for someone interested in starting deep sky astro photos?

The only experience Ive got with astro photos so far is taking planets and the moon with a Phillips Toucam.

Post by **weixing** » Mon Sep 10, 2007 2:28 am

Hi,

'm currently using a C8 and an 80mm f/6 widefield scope so I think scope wise I'm ok, but my mount - an Orion SVP has not been performing very well (visually ok, but photography is really pushing it when I tried to use a DSLR w e 80mm)

I think SVP mount and 80mm F6 scope should be ok for unguided Astrophotography if you done a good polar alignment. Did you do drift alignment?? It's basically a must if you to do decent Astrophotography.

What would be a good mount to consider and what CCD camera is recommended for someone interested in starting deep sky astro photos?

IMHO, you already got all the equipment to start learning Astrophotography. Just go out and shoot some image and learn image processing. With more experience, you can make better decision on what you need.

Have a nice day.

jermng · Post by **jermng** » Mon Sep 10, 2007 3:21 am

Thanks Weixing.

You are one of those who advocate using what you already have and make the best out of it which I really appreciate.

Anyway, a second question, I notice there are 0.5x focal reducers available from OPT and Agena etc. Does that mean my f/10 will become an f/5 and f/6 will become f/3? In that case, what's the diff. between this and the typical SCT .63 reducer other than the .63 mainly used for SCT?

Post by **weixing** » Mon Sep 10, 2007 9:24 am

Hi,

Anyway, a second question, I notice there are 0.5x focal reducers available from OPT and Agena etc. Does that mean my f/10 will become an f/5 and f/6 will become f/3? In that case, what's the diff. between this and the typical SCT .63 reducer other than the .63 mainly used for SCT?

Some of this focal reducer are intended to use on small chip size CCD which may cause serious vignetting when used on a bigger size chip, such as APS-C (non full frame DSLR). Also, some of them may not work on Refractor and Newtonian due to the limited focusing range.

The standard F6.3 focus reducer/flattener are design to work on SCT and SLR camera, but may also work well on Refractor. But there are also limitation especially when you try to get a very "fast" f-ratio with it... you may get away with small chip size CCD, but may have serious vignetting and aberration when use on visual or with bigger chip size CCD.

Anyway, it best is to check with people who had use this type of focal reducer first.... I think someone in SingAstro had a ATiK 0.5x focal reducer in the past.

By the way, the final f-ratio will depend on the distance between the focal reducer and the focal plane. For example, some 0.5x reducer will give a 0.5x for photographic use, but only 0.7x for visual use.

Below is a link to Sky and Telescope website on this:
http://www.skyandtelescope.com/howto/as ... wAll=y&c=y

Have a nice day.

PS: Hope I give the correct information as I'm still learning too...

Meng Lee · Post by **Meng Lee** » Mon Sep 10, 2007 10:16 am

In my opinion, all focal reducers will work with all kinds of scopes. The only difference is that whether your focal plane will become flatter or more curved. A dedicated focal reducer will make the scope faster and flatten the field. Imagers also use focal reducers to match the pixel size to the sampling resolution, typically 2.5 arcseconds per pixel. If the matching is not done properly, then you will have big fat stars even for not so bright stars.

Also note focus issues when you use focal reducers that have too high power like 0.5x.

Skyview Pro seems ok to me, just get the polar alignment done, use better motors like their GOTO kit motors. and the scope at most 100mm, then you should have nice pics from your DSLR.

Post by **weixing** » Mon Sep 10, 2007 11:21 am

Hi,

and the scope at most 100mm

Err... you mean 1000mm?? I had not try unguided for more than 1000mm, but had try 1000mm unguided on both my GP (previous) and GPD mount with decent result.

Anyway, I'm also interested to know is it possible to do unguided for focal length more than 1000mm (especially 1280mm... C8 + f6.3 focal reducer) for at least 1 minute exposure. If it is possible, I may had to rethink my current setup as I'm overloading my mount and may be myself... hee hee

Have a nice day.

Meng Lee · Post by **Meng Lee** » Mon Sep 10, 2007 11:31 am

Oops, I mean 100mm = 4" aperture scope.

I believe the max astrophotography loading on the mount = 60-70% of the recommended visual loading otherwise, light wind will send the whole system shaking more than 1 pixel.

I think its possible to achieve 1280mm with 1 min unguided. Dirift alignment must be very good, balancing must be very good and there must be no wind. Perhaps, about 1 in 8 frames will be ok?

But I think the mount should be a larger one if you are going beyond 1000mm, G11 with C8 should be good. Hehe, my cresecent neb was taken at around 700mm. Let me try next VC 200L with reducer on EQ-6, that will go beyond 1000mm.

jermng · Post by **jermng** » Mon Sep 10, 2007 11:58 am

Thanks Meng Lee and Weixing.

Meng Lee, how do u calculate how many arc seconds per pixel? Is there a formula? What is the "maximum tolerance" to arc seconds/pixel? As in wats the biggest number before you get big fat stars?

Thanks again.

Meng Lee · Post by **Meng Lee** » Mon Sep 10, 2007 12:22 pm

theoretically its 2-3 arc seconds per pixel. But as a start, don't need to worry about that, just start taking pics. Later on, when you going into high res DSO imaging, then worry about that. Just try any configuration first

jermng · Post by **jermng** » Mon Sep 10, 2007 2:47 pm

Thank you!