How much softening with a Powermate?

[SJP]

I got my telescope just after Christmas, and had some success with DSO astrophotography during the winter months, but have recently turned my hand to planetary stuff.  Whilst I was initially quite pleased with my results after investing in some bits and bobs (Televue 5x, Celestron NexImage 5, Celestron 3x Barlow), over the last few weeks I've found the images to be very soft and lacking in detail whether I use my DSLR or the Celestron NexImage5 camera.

This morning I set the 'scope up trained on a TV antenna and took a series of grabs through a DSLR.  The images are shown below.

My question is this : Obviously, putting supplemental elements into the optical path will degrade image quality (and will make focussing harder), but is the sort of softening I'm seeing normal, or should I be looking elsewhere for the cause of my lacklustre planetary performance?

First, DSLR/lens at 400mm as a baseline - pretty good, sharp, contrasty, and generally wholesome

2x200mm by S.J.P, on Flickr

Next-up is with the DSLR attached to the 'scope (T-Mount adapter) with a focal length of 750mm.  Image is still OK, a little less so than the 400mm shot, but still quite good.

750mm by S.J.P, on Flickr

Next I tried the DSLR with a 2x Teleconverter (Extender), giving approximately 1,500mm FL.  Things are still reasonable but sharpness and contrast are beginning to suffer just a little.

2x750mm by S.J.P, on Flickr

I then switch to the Televue 5x, with an approximate focal-length equivalent of 3,750mm, and things soften-up markedly.  Obviously there's vignetting too with the 1.25" Televue, but the loss of contrast, detail, and sharpness really surprised me.

5x750mm by S.J.P, on Flickr

I also tried eyepiece projection through a Hyperion 5mm (150x), and I wasn't surprised that this gave the softest, least contrasty result of the lot.

5mm EP Projection by S.J.P, on Flickr

[Leveye]

For the kind of glass your using and the quality you get in this price range that's more than except able in my book. Try a Powermate with a T-ring.

[SJP]

Good to know there isn't a problem with what I have, besides inherent limitations! BTW I was using the Powermate with the T-Ring adapter.

I've done a bit more comparative work this afternoon, using the Celestron 3x Barlow and TeleVue 5x Power-mate with the NexImage5 and am amazed how much "wobble" is present even over short distances It's also staggering how much more "magnification" I get from the NexImage5 vs. the DSLR (guess that's down to 2.2um vs 6.8 I'm pixels!)

It seems that the Powermate is much harder to focus accurately, but the stacked images look better when everything is perfectly set up.

Can't help but think that my successes with the Celestron 3x Barlow are down to it being easier to focus!

[Geordie mc]

Did you use mirror lock up? Might sound obvious but thought I'd mention just in case.

[davefrance]

It looks a little better with the CA removed and sharpened a little. At the magnification you are trying to use a rock steady tripod/mount and remote shutter release are a must and as already mentioned, mirror lock up. Don't think you mentioned what your scope is but depending upon the optics perhaps you are asking a little too much?

[SJP]

'scope's a basic Celestron 6" Newtonian, so possibly I'm expecting too much!

I shot in LiveView (so no mirror movement issues) and was using a remote release as well.

I've posted another thread (about Saturn images) in which I was after some advice on sharpness, and tried some terrestrial images as well (this thread) .

It's just useful to know whether I'm missing something, or whether I'm at the limit of basic equipment. 

[PeterCPC]

That's a really good comparison - thanks for posting that.

Peter

[Hugechris]

Great comparison. I guess your scope is well collimated?

Sent from my iPhone using Tapatalk

[ollypenrice]

I admire your rigorous approach, empirical and yet informed by an understanding of the theoretical issues. With this approach I'm not sure that you need the forum - though you are most certainly contributing to it!

Oly