First Attempt - Need help!

[scitmon]

On 2/6/2018 at 11:29, happy-kat said:

3 - let you histogram drive your iso selection, review your test shot and aim for the histogram peak to be clear of the left edge, most likely will be either 800 or 1600 iso.

 

I find this comment very intriguing.. I understand the need for getting the peak of your histogram clear from the left, but what would the pro's and cons of lowering the ISO to, for example, 200 for a longer exposure be to say 800 for a shorter time? (sorry if i'm hijacking the thread).  I used a modded Canon 700d and have read to use ISO 800 or maybe 1600 only.

[catburglar]

The ISO setting in a DSLR is analogous to the gain setting in an Astro camera. Generally noise will be higher as ISO increases and dynamic range will be reduced. There’s always a balance, lower ISO for longer exposure time will generally give better data to start processing but longer exposures are more taxing of the mount etc. 

[happy-kat]

Local conditions play a part too, if I don't use a filter then my ISO is 400 to get the histogram clear from the left and 800 is too far to the right. That's my local conditions dictating what I choose. 

[scitmon]

By local conditions I'm assuming you mean light pollution and brightness of the target? 

I was imaging M31 a while back and found I only needed to capture around 60 second subs at ISO 800 to get the histogram clear from the left, which made me wonder what the point of buying a guide scope was?  Would you say in situations like these dropping the ISO to maybe even 200  for longer exposures would be beneficial?

[happy-kat]

I'm limited in exposure length so I have to pick the ISO for local light pollution and exposure length limitation experienced on the night.

I have the same limitation as the OP who started this topic.  If you can expand onto guiding you don't have these limitations but have the advantage of taking longer subs even doing this at 60s.

 

 

[Skinnypuppy71]

I didn't think I would be able to do any kind of AP with the skywatcher star discovery mount which I own along with a 150pds....so is it actually worth purchasing the required t mount and adapter for my olympus micro 4/3rd 's camera..or even the L bracket to attach my camera and 12-40 f2.8 lens to the mount...I know long subs are out of the equation but would I manage 30-60 sec subs at say 800-1600 iso.....and not get trailing?

[happy-kat]

You would enjoy reading the "no eq" dso Challenge thread. How much does the 150p-ds weigh?

You could use you camera and camera lens to good effect I think.

[Skinnypuppy71]

The 150pds is around 100g shy of the recommended 5kg max payload of the mount.but it seems to cope quite well slewing the scope around.

[happy-kat]

Add your camera and it would be over plus any slight breeze and the telescope would catch it, I'd start with your camera and lens it would probably be less frustrating initially.

[Skinnypuppy71]

So would I need a L bracket and ball head or a dovetail bracket to attach my camera to the mount....oh and thanks for the response it's very helpful.

[happy-kat]

You don't have to use a ball head but a camera flash hot shoe mounted red dot finder would be useful for goto alignment. I got mine from astroboot others have got just a shoe fitting of ebay.

If you use a longer lens then a ball head could help with balance.

[happy-kat]

Check out the price differences for both options either your Sony t ring and t mount versus the l bracket and perhaps decide from there and if you want to use your sony with telescope on the Moon you'll want those adapters anyway.

[Skinnypuppy71]

My camera Is a olympus omd em5 mk 2......not a Sony, happy cat, unfortunately.......I wouldn't mind a Sony mirrorless right enough...the thing I'm kind of struggling to understand at the moment..Is if I attach my camera via the various adapter /t mount.......I'm using the telescope as the lens,but yet...nothing is actually magnified...unless I view through a eyepiece....so my camera is basically seeing the sky via a couple of mirrors.......does the focal length of the telescope have an effect on magnification?sorry if this seems a dumb question but when I want magnification for my camera....I need glass.lol.

[Stub Mandrel]

The telescope acts exactly like a telephoto lens of the same focal length, but it probably has a greater aperture than an equivalent tele lens so more light gathering power for faint objects.

 

[FlyDoc]

In an effort to improve tracking accuracy I am going to get a 12V adaptor. Does anyone know how much does Star Discovery mount draw? 

Also looking at a DSLR red dot finder, does anyone have any recommendations?  This looks promising but not sure where to get it https://www.astroshop.eu/red-dot-finder-scopes-led-telrads/astoptics-red-dot-finder-for-dslr-hotshoe/p,48281

Thanks!

[Skinnypuppy71]

Hay Flydoc...when you say a 12v adapter...do you mean a power tank.....if so...I don't know what kind of power the mount draws but I'm currently using the  phase 4 in 1 17 ah jump starter power tank from Halfords....it has two 12v sockets and is less expensive than skywatcher or celestron's own offerings...maybe not as focused on powering mounts etc but is over half the price and is holding up well so far.

[happy-kat]

I'll add some red dot finder links later as can get much cheaper than that.

[happy-kat]

It really does help other members help you if you put at least a country in your location please.

Astroboot camera flash hot shoe mounted red dot finder. Link here

Ebay ready printed idea. Link here

Thingverse something like this and get it printed locally. Link here

[Stub Mandrel]

Or you can 3d print this to tide you over for now, works well for short lenses, fits in the hot shoe bracket:

Finder.stl