DSO Beginner Imaging Question

[Leedsgreen]

Dear All,

I am keen to use my SkyMax 127 to try and image some (bright) DSOs and have a few questions:

1. If I'm correct, the way to reduce the FL of the scope is to attach a focal reducer. The best way is to buy a converter that attaches to my Mak and allows a f6.3 SCT reducer to be attached?

2.If so, is there any one better brand of reducer (i.e. Meade or Celestron) or is it OK to buy a cheaper generic one?

3. How do I attach my DSLR to the scope with the reducer attached? I already have a T-adapter for the camera, do I need to buy a another stepping ring that converts the thread on the reducer to a T-thread (or is it already a T-thread)?

4. Is it possible to use an extension tube at this point to increase the focal reduction (i.e. to make the Mak f5)?

5. If all this works and I manage to have Mak working at, say 750mm FL, with DSLR attached, will it be possible for me to image some brighter DSOs? I should add that I only have an Acuter Merlin autotracking mount but I believe that so long as my exposures are under 30s (and the mount is well aligned) there should be little trailing?

6. If so, is 30s enough (at ISO 800) to capture images (to process in Deep Sky Stacker)?

I would appreciate any help/advice with the above. I realise there are some limitations to my set-up but am keen to try and see what I can do fairly cheaply.

Thanks very much,

Nick

[jgs001]

Nick, I can't comment on the Focal Reducer questions, but for the last one, tracking in AltAz, the limits on trailing vary depending on where in the sky you are attempting to image. Apparently Focal length has no bearing on the tracking time, but it will magnify any drive errors. If you image low down in the east and west you can extend the imaging time, but as you get more to North/South and overhead the duration reduces. I have imaged for 2 minutes, tracking in AltAz, low in the east. You'll have to experiment really and find out what sort of sub lengths you can achieve. 30s at ISO800 can capture a fairly significant amount of information, but expect to have to take a large number of them. I think my record was 154x30s subs. At 132x40s I got the Bubble nebula showing on the stacking image with an unmodded camera. What camera do you have ?

[Leedsgreen]

John,

Thanks for helpful reply. Actually, I 'have' my friends Canon 400D (unmodded), which is a lovely camera (although there is no live view so I imagine focusing will be more difficult)? I know this can go up to ISO 1600, so that might also be an option. If funds allow in the future (or I can encourage my friend to upgrade!), I have in mind a 500D, which has even higher ISO.

Would something like M31 be a good place to start and possible with my set up?

Thanks,

Nick

[jgs001]

Nick, to be honest, M31 is what I used with 2 minute subs I'd start with clusters to be honest, they don't need the long exposures. The Mak will probably do a very good job on Globular clusters without the focal reducer. I don't know the 400d, but 1600 may be a bit high, start at 800 and see how you go. You'll need to experiment somewhat.

[Ant]

The trouble is the MAK is what F15 (maybe F13)?

I have a Skymax 127 and the focuser hole is quite narrow, with a large chip dSLR (like the 400D) you will get some vignetting (darkening at the corners), but you should be able to get some pleasing results!

I used a cheap Skymax => SCT thread adapter, these aren't expensive. Then I added in a F6.3 Reducer (I had a Meade version, but I beleive that the Celestron one is better). Then lastly I bought a cheap SCT =>2" adapter.

The 400D fits into the 2" adapter (with a T ring and 2" adapter).

That did work but did still suffer from sligh vignetting.

If you need links to the adapters I used let me know.

Cheers

Ant

[Leedsgreen]

Thanks very much for further replies. Ant, yes, please could you attach links to the adaptors. Whilst I understand how to link reducer to Skymax with SCT threa adapter, I'm unsure about necessary links from adapter to DSLR (I currently have a DSLR adapter that offers a T-thread).

Also, could you give an indication of the extent of vignetting? Is it possible to deal with using flats (or whatever in deep sky stacker) or cropping the image somewhat? I'm not after perfection (well, not most of the time!) but would be good to know.

Finally, is it possible to add 1.25" diagonal to scope with SCT reducer in place (i.e. so I can use my eye-pieces)? If so, how is this achieved?

Thanks again for any help,

Nick