Astro Photo help please

[Swamp Gas ?]

With a very limited budget I am trying to take some decent lunar photographs using a Minolta A1 digital camera connected directly to a Baader Hyperion eyepiece with a 43mm-49mm step up ring.

I have to zoom in ( which extends the camera lens a good 2 inches - meaning I have to use a bracket to take the weight of the camera off of the EP ) before I am able to bring into focus with the telescope focuser.

But by zooming in I get the typical "down the rabbit hole" results ( I think the tech term is vignetting ? )

Does a "focal reducer" get rid of this problem or is there another technique I should employ ?

At present I have to crop major amounts from each shot - only the very center of each is usable.

[jgs001]

I was suffering the same thing with my Z2. The objective lens of the Z2 was just too large for the exit pupil from the ep. Zooming in helped but the vignetting was always appaling. An FR will probably work, as the magnification will reduce and I think that increases the exit pupil. The other option would be to use a longer focal length ep, which will have the same effect.

[Swamp Gas ?]

The problem I have is that the camera will only attach to the baader - my other ep's would require different methods.

I'd like to get around the problem somehow using the baader as I have the expansion rings and it's like having three ep's that can be attached.

Here is an example from a couple of months ago.

This is already heavily cropped , yet the vignetting is still awful.

[Milamber]

Have you tried it with the barlow off the end of the EP (i.e. in 2" mode)?

Arthur

[jgs001]

Apart from th vignette that's a superb result, well done

[Swamp Gas ?]

Have you tried it with the barlow off the end of the EP (i.e. in 2" mode)?

Arthur

Do you know - I never thought of that !

I'll let you know how it goes.

Big thanks for a possible easy solution

[Swamp Gas ?]

OK - Probs - How do I dismantle the Baader Hyperion to remove the barlow whilst keeping the 1.25 fitting ? - I don't want to screw my best ep but so far the barlow lens within seems fixed inside the 1.25 attachment - and the moon is looking so photogenic right now !!!

After taking that join apart I am now brushing out the dried glue that sealed those bits together - snow storm in an EP - aggghhhh !

I'll get something tonight - no matter , but it feels like something just keeps throwing spanners at my attempts at real imaging !

This is why I just watch !! - Tech is good but you miss so much setting up all this "cool modern" $h1t.

[jgs001]

The barlow element is fitted into the 1.25" fitting. The entire thing, the silver section on the bottom, unscrews from the body, the black portion. The EP then becomes 2" fitting.

[Milamber]

... err, which bit did you unscrew? The white storm's got me worried!

[Swamp Gas ?]

... err, which bit did you unscrew? The white storm's got me worried!

No worries - it was just some kind of locking adhesive. Brushed out ok - and the slightly tacky inside covering of baader ep's should take care of any bits I missed.

Anyway - yes I end up with a 2" ep - but I only have a 1.25 focuser - If I could remove the barlow from inside 1.25 attachment it might work but I'm hesitant of going any further - limited funds stops me from taking any risks with my main ep.

[dph1nm]

Note there are two different effects here. True optical vignetting and well, just field of view cf the eyepiece size. The latter is what you see if you just stick the eyepiece onto your camera without the telescope. Usually you will set a sharp circular image, which often doesn not fill the camera field of view. Zooming in can help with this. This is usually called vignetting in digiscoping circles, but it isn't really!

I think the above effect is why people complain about "large lenses" being no good for afocal photography because they are "too big for the exit pupil". This is not true (my 135mm SLR lens works just fine but is much bigger than any digicam lens), especially not in digicam zooms where the large lens aperture is not used expect at full zoom. The opposite is usually the problem - digicam apertures are too small for the the exit pupil and so you effectively stop down your telescope. For instance at its widest , the Minolta A1 has only a 2.5mm aperture at f2.8!

Real optical vignetting is the "fuzzy edge" effect where the brightness of the image drops of gradually towards the edge. This is due to a mismatch between the spatial position of the exit pupil of the eyepiece and the "input pupil" of the camera lens. You just have to get a lucky combination of eyepeice and camera to fix this.

Note that two are not really related. So I tried out a Hyperion eyepeice on my camera before I bought it and the sharp circle of light filled the field of view. so I thought, great! But putting on the telescope I get loads of optical vignetting, making it useless for afocal photography.

NigelM