Beginning in AP in Singapore - Equipment Questions

[ebeyonder]

Hi all,

I am keen to pick up astrophotography and have bought some equipment here in the US. I am returning to Singapore next year, so my equipment are really meant to be used in Singapore in the long run.

I had originally planned on a light 80ED, but ended up with a WO FLT-110 TEC (715mm, f/6.5) instead. Because of the original plan on the 80ED, I got an Orion Sirius EQ-G mount.

The Sirius mount is rated at 30 lbs. I understand from here and other forums that for AP, the rated weight capacity should really be halved or at most used at 2/3 capacity.

The FLT-110 with rings, focuser and an Orion Starshoot Pro cam weighs in at about 20 lbs - already the 2/3 limit. I plan to add a guidescope - originally wanted a ST80 but have now decided on the KWIQ or 9x50 finderscope to cut down on weight.

So all in all, I am probably looking at about 22 lbs on a mount rated at 30 lbs. No doubt a bit heavy for AP from what I have read!

I have some questions which I would be grateful for any help:

1. I think I read that because of Singapore's light polluted skies, long exposures are not feasible even for DSOs. Instead the trick is to take shorter exposures of DSOs and then stack multiple images together - is my understanding correct?

2. If that is correct, do 5 mins exposures sound ok for DSOs? I read from CN forums that someone with a similar set-up as mine was able to get 5 mins out of his Sirius mount before he had to throw away exposures excessively. So if the Sirius can do 5 mins exposures without great difficulty, would stacking these images together work in Singapore skies?

3. Would the KWIQ/finderscope guidescope option work in Singapore skies? Would it be too small to spot guidestars?

4. I have also read about this program known as WCS which allows drift alignment to be done via a CCD camera and on the computer. I am thinking of using this with an old DSI I have. Does anyone have experience with this in Singapore?

The main advantage of the Sirius mount is that it is light. But I have read from the experts here that if one wants to AP right, then weight should not be an issue. Since I may be able to get these mounts cheaper while I am in the US, I am keen on getting the right equipment before coming back to Singapore next year.

Looking forward to all your comments

Thank you!

[rcj]

Hi,

Must be the lucky one to answer your questions first, anyway my replies (IMHO) are as follows:

If you are into astrophotography, the mount that you have should be over-rated. This helps not only to provide stability for guiding and (hopefully) keep vibrations to a minimal, but at the same time provide an avenue of growth for you to get bigger OTAs in the future if you find that imaging is what you like and can do. Again, everyone has his/her own pace, so get a mount that suits you, your budget, and your needs. I will avoid commenting if the Sirius is the best mount for you, as you should be able to get ample information from internet literature fairly easily these days.

Adopting 5-min subs is a sensible choice for a 4-inch refractor and the imaging camera you have assuming capturing from Singapore. Personally I have been using 5-min subs for light frames via the ccd camera from Eunos, but occasionally when the skies are more transparent, it is possible to go up to 7-minutes. For H-A, 20-min subs are not uncommon. The length of exposure will also depend on local light pollution in your area. You can go longer exposure if your camera has a greater dynamic range even with substantial light pollution since a greater dynamic range will also enable you to be able to stretch your stacked DSO image to a greater extent without being 'grainy'. So the main idea here is to best experiment with how deep (long) you can go for subs duration and then use that as a start in getting a set of light frames for stacking later.

One limitation of embarking on longer exposures would be the need to consistently obtain predictable tracking behaviour for your mount. Note that this does not mean a mount with high PE will not do well, but it is certain that a mount with high AND unpredictable PE patterns will make autoguiding more tedious and 'less clean'. Again, it helps to maintain the mount properly, keep the gears meshed properly and also clean them regularly, ultimately the idea is to get consistent predictable tracking without big erratic humps in the PE curve profile.

The KWIQ/finderscope option should work with the FLT110 at native focal length. There are many out there using 50mm finderscopes for guiding with 500-800mm F.L. type of refractors.

No experience with WCS though. If you can drift align in less than 10 minutes, the manual way should be faster. But do let us know the results and experience if you are keen on using WCS.

It would be a great choice to get the equipment if you are physically in the US, you save the shipping and with the low USD dollar now, it has never been a better moment. However, don't land up with excess baggage charges!

Cheers,
Remus

[ebeyonder]

Thanks very much for your reply, Remus

I've read conflicting things about the Sirius mount but I think I'll keep it for now to see if it works for me. Also, being portable, it's definitely easier to learn the ropes with too (and as I've realised, there is a LOT to learn!).

I think I'll go for the KWIQ scope too. I thought of converting a finderscope myself, but it seems to be a real hassle finding something that fits and something that can reach focus with.

I have never done drift alignment before so I thought WCS would be a great tool But maybe I should learn how to do it manually as well.

Many thanks again, and if I may say so, your pictures are outstanding! Hopefully one day I can reach a fraction of your quality.