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Robbrad

SkyWatcher 150p (A few years on)

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We moved house to a Bortle 5 location which is great. The last three nights have been incredible conditions, which led to my frustration more so. I did manage to capture a decent beginners shot (1st image stacked in Photoshop 5x30seconds at iso 12800)- couldn't get DSS to work) of M42 but i'm still not happy. Im thinking my 750mm telescope might be to long.

I have an EQ3 mount and a 25mm eyepiece (Cant even get the 10mm to focus on stars) with a D750 camera attached(focusing was hard but managed it with a bahtinov mask - 2nd image of Sirius)). I can't get the scope and the camera to balance when RA and DEC are open with the DSLR attached, so I attracted some extra weights which balanced it, but resulted in trails.(3rd image) !!

So I removed the weights and did a 2 min exposure, (ITS AVERAGE! to say the least) it's still not as tack sharp as I was expecting and the edge stars look odd - feel like it does not match the effort I put into polar aligning, focusing etc

As for other objects nothing really showed up on long exposures

Have I reached the bounds of my equipment ?  The end of my tether... the edge of sanity 

Any suggestions before I spend a load of money or give up ! (Appreciate patience is key but I feel like im doing everything right but somehow something isn't going well, or the scope is out some how)

Thanks in advance

Rob

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20190227-22_34_14_-DSC_3883.JPG

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If you're going to do eyepiece projection, you're going to need a better eyepiece.  That 25mm appears to have edge of field aberrations dominated by chromatism.  It may also not be projecting a flat field onto your sensor leading to the bloated stars at the corners.

Have you tried prime focus photography yet?  The camera is attached directly to the focuser via an adapter for that method.  You may need a coma corrector if your telescope is a Newtonian design to correct coma and flatten the field.  Since you don't specify what your scope is beyond having a 750mm focal length, there's not a lot more that can be said on that subject.

You're discovering why folks opt for an HEQ5 mount as a starter mount for astrophotography.  It has the load capacity that an EQ3 just doesn't have.

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Thanks Louis! I am doing eye piece projection...

The scope is a skywatcher 150p (sorry I put that in the subject)

so I can connect my cam direct to the focuser? What adapter do I need for that and do I need a coma corrector and a field flattener if doing that?

looking like I need a better mount...

thank you

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Rob

You should be able to connect directly to the focuser using an adapter - is the D750 a Canon model?

When I bought my 130P it came with a Canon fit adapter which I have no use for - I would be happy to post it to you (provided I can still find it).

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Hi Rob. Looking on the optimistic side, you have images and can identify the problems.

As Louis suggests, a stock 25mm eyepiece is not going to give good results.
Putting the camera direct on the focus tube means the only optical components are the primary and secondary mirrors.
I am sure this will improve things for you.

You need to be aware of the path length. The camera sensor may be further out than the eyepiece.
This means you need to rack the focusser well in. Which has the advantage of giving a more rigid fixing.
You can try this in daylight with a distant object to make sure you can reach focus. Some scopes won't do this without work - but think about this if it happens.

The multiple diffraction spikes showing on Sirius are coming from things other than the secondary mirror supports.
Worry about these after you have simplified the situation by using prime focus photography.

The lower exposure trails are caused by a fast mount movement. Probably backlash in the mount.
Balance and backlash are big subjects.
If you keep the mount only a little bit off balance and stay to one side (hemisphere) it will take up drive backlash and improve things.

I'm sure that even with an EQ3 mount, you can improve the situation and you will learn a lot on the way.
Do this before reaching for your wallet.

We all have similar photos in our collections. It is just that we are not brave enough to post them!

Hope this helps and encourages, David.
 

 

 

bright i

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Wow thank you guys some fantastic advice and inspiration.

I have had this kit 5 years and never realised you could conned the camera directly!!

Now I just need some clear nights again and I’m gonna try this out.

Then fine tune the results as you described.

B61CB510-1FDA-4DC5-A22E-98EBE27A09E7.jpeg

Edited by Robbrad

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As above, practice during the day when you can see what you are doing.

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2 hours ago, Carbon Brush said:

The multiple diffraction spikes showing on Sirius are coming from things other than the secondary mirror supports.

 

10 hours ago, Robbrad said:

focusing was hard but managed it with a bahtinov mask - 2nd image of Sirius

Spikes are due to the focusing mask.

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Posted (edited)

Sorry for the delay in reply and im afraid more advice needed. Finally some decent clear skies.................

As advised cam attached direct to scope ! - thank you FOV looks better as I can now get in the full field of some objects - although Andromeda looks a bit small.

Issues im facing

  • DSS won't stack (as I think the image isn't sharp enough) - this is my pursuit now. Without stacking I can't hope to get decent images or move to fainter objects.
  • The stars look like little zigzags - Tracking issue? polar alignment? - scope was steady and balanced
  • Images attached have been edited but my images are blown out on exposure (attached one example - 3200 iso @ 30 seconds)
  • Stars are a little stretched at edges (is this due to the refractor?

Thank you

Rob

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Edited by Robbrad
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Posted (edited)

Hi Rob!

Nice progress you have there! The star trails might be a tracking issue. How accurate is your polar alignment? Do you use an intervalometer to avoid any shaking during imaging? I suggest you to use a little lower ISO for less noise in the image, personally I use ISO 1600 while imaging with a DSLR. This will also help with blown up images. Andromeda is actually much larger than what is visible from a single exposure. Stacking more images will bring out the fainter detail.

The stretched stars near the edges are caused by coma. This is normal for Newtonian telescopes and can be fixed with a coma corrector.

Cheers, 

Tomi

Edited by AstroFin
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Posted (edited)

With proper balancing and polar alignment, EQ3 pro can bring decent images, it actually depends on your camera haha... Check out drift alignment as it is the gold standard to get polar aligned, and you could get 30 seconds with no star trails I believe. And identify whether the stars are drifting on right ascension or declination. IMO, try lower ISO like 400 for my D5300, play around with the parameters to get the optimal settings. Remember to take calibration frames as well.

Image attached is M42 taken under Bortle 8 skies, with EQ3 pro, D5300, 150p and total integration time is 40 minutes. With your dark skies, you would get much better images! Hope that helps and all the best!

m42final.jpg

Edited by ZiHao
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Thanks for the inspiration guys. I have taken the plunge and bought the ZWO ASIair and the ZWO 178MC. Appreciate this won’t fully resolve my alignment issues - but might be a bit more fun than the clunky DSLR.

I was using a remote release for the photos with the SLR and mirror lockup. Thanks for the iso tips.

I'm finding polar alignment a challenge. Is there any more info and drift alignment. I think I have screwed up the calibration of my polar scope.

 

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7 hours ago, ZiHao said:

What a fantastic technique! That makes a lot of sense.

 

My only issue is the house is in the way due south. So I won’t pick up a star with zero dec. I guess that’s gonna matter as the target result won’t be a flat line. Any tips as I’m in the U.K.

Lots of sky available north and west

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Posted (edited)

http://www.astrosurf.com/re/polar.html

Here it says you can pick stars from +20 declination, is it high enough to be visible from your imaging location? If not then I think you should try to fix your polar scope (no experience of polar scope as I don't use it). 

There's another method as well to get a decent polar alignment during the day. Install an inclinometer app on your phone and then place it on the dovetail saddle, adjust the altitude bolt until the reading matches to your location's latitude. 

For azimuth, you can either use a good compass or this method here https://www.youtube.com/watch?v=rPdQ9pU9GJA

Anyway, just try out different methods and see what works. HTH.

 

Edited by ZiHao
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