Focusing as usual!

[Snaggerman]

Hello,

After mooching at this forum for a long time I have taken the plunge and signed up!

I probably have one of the most modest set-ups around, apart from my (basic) DSLR camera, I have so far splashed out the princely sum of... £31.50p. This has however bought me two telescopes, a smattering of eyepieces, a barlow 2x, and a T-mount that I have spliced on a Pentax K-mount bayonet fitting.

I am happy with this gear however, as I am keen to understand exactly what is going on (or wrong) before I do any kind of upgrading. My current area of interest, you may be surprised to learn, is the moon. It's big, bright, and very interesting.

With my more basic scope I am getting a nice picture of the moon (I've tried to attach it here) but it's nowhere near as good as the view through the eyepiece, so I know that the scope is way better than my photo would suggest.

My question is how can I get a similar result on my camera that I see through an eyepiece??

[Neil McRae]

Hi Matt

My experience is that you (or at least I) dont get on camera what you see through the eyepiece. I have several "good images" of the moon taken with webcam and DSLR and although I am pleased with them I always find that when you look through the eyepiece the image is always sharper.

Hope you dont mind but I ran your shot through photoshop and tried to sharpen it a bit. See if it looks any better.

Clear skies

Neil

[Shibby]

The eye is a wonderful thing, it can adjust for slight errors in focus. An imaging sensor is totally different, the light needs to be *perfectly* focused because your camera is totally unforgiving.

The answer is a focusing mask; Bahtinov masks seem to be the most popular. I made one myself from a piece of card.

[JamesM]

Technically it is possible to take a photo of the moon with a single shot from a DSLR if you happen to press the shutter when our atmosphere is still. Under normal conditions however, you won't be able to take a sharp image because you are imaging through atmosphere (termed 'seeing') which boils or distorts the target. Your image is relatively small so these effects are hardly noticeable but as you ramp up the magnification, the effects of blurring will increase. It is for this reason that people use a webcam, that will record a large number of frames in a very short period of time in order that they can select the best of these frames to 'stack' together and so construct a composite sharp image. This technique can also be used on planets as well but not any on any deep sky object like nebula, galaxies etc. These objects are faint and so need some form of accurate tracking to hold the image precisely in focus over a period of time in order to collect enough light (data) from the image to again stack and improve in post processing software programs. To track accurately enough for imaging you will need at least a HEQ5 mount that will also facilitate accurate polar alignment. Webcam images can be taken from scopes that have no tracking capability which are aimed at bright objects like the moon and planets.

Hope that helps

James

[Snaggerman]

Thanks for your replies - I'm still puzzled:

Seeing was pretty good when I took the shot.

The image on the eyepiece was much clearer, by a factor of about 5x I reckon. It was also much brighter, I was quite taken aback when I swapped back to looking through the eyepiece.

I had a good go at focusing, tweaking carefully, my best three shots were pretty good, but still nowhere near as good as the eyepiece view. I don't think I could have got it any better even with a mask.

I noticed that my T-mount brings the camera much closer to the body of the telescope and that there is a small extension ring on my eyepiece, I thought that I would run out of focus without getting the DSLR chip within range of the incoming light.

I think I just don't understand what work the eyepiece is doing? And why I should lose so much light going through the camera, I don't seem to lose much if any with any of my other photography?

Thanks again

Matt

[Shibby]

The brain is also a wonderful thing It processes an analogue stream of visual data to form an image of what you're looking at. This means that as the image varies due to seeing etc, you will be seeing more than the camera at any one instant. Not dissimilar to stacking to be honest!

Having said that... The seeing is good enough that it should be possible to get a sharper image than you have. (the whole moon fills a wide field) I've seen some very sharp single exposures of the moon.

Focus is one possibility - you simply can't focus manually as well as you can with a focusing mask. Another possibility is camera shake. Are you using a remote shutter? Does your camera have a mirror lock function?

It was also much brighter, I was quite taken aback when I swapped back to looking through the eyepiece.

...

I think I just don't understand what work the eyepiece is doing? And why I should lose so much light going through the camera, I don't seem to lose much if any with any of my other photography?

My knowledge falters a bit here... but I'm pretty sure that at prime focus, your focal ratio is much faster than it would be when projected through pretty much any eyepiece. That means that the image should almost always be brighter *without* the eyepiece... I'm sure others will correct me if I'm wrong.

[Sparrow]

As Lewis said, the eye is a wonderful thing - it is able to resolve much finer detail than a camera - where the camera can win over is sensitivity in the dark - such as for long exposures of very faint deep sky objects that the eye just can't see. For a bright object like the moon, the eye is acting with a very fast "shutter speed" and can see the finer sharper detail. The way imagers get round this to get a razor sharp image is twofold:-

1. An good moon image will be made up of not just one shot but many - perhaps even hundreds. This is then run through software such as Registax to "average" out the image - this helps to get rid of atmospheric distortions caused by air movement and heat haze.

2. Higher focal length to image portions of the moon and then "mosaic" it. The finished result is a high resolution image which has the sharp detail.

ALthough most of my imaging is deep sky objects using a DSLR, for imaging the moon I still turn back to my little Meade LPI camera - similar to a webcam - because of the magnification this gives me, I need to take about 30 panes of the moon each comprising of many subframes. I then mosaic them to give a high resolution image of the moon. This gives me a result far superior to the DSLR - surprising I know when the DSLR is technically the better camera with higher resolution.

Hope this helps

Regards

John

[Psychobilly]

All my crispest shots have been mosaics with the DMK.. usually 1000-1500 frame captures per pane...

When I used to shoot moon shots with the DSLR I would rack the focus back and fore around the "optimum" focus point in small movements (onthe fien focus of the 10:1 crayford) taking a shot at each position and then going keeping the best...

Peter...

[Neil McRae]

Sparrow has good advice creating a "mosaic". You can use Microsoft ICE (it is a free download" and stitch several images together. I have used this and get good results.

One (might be obvious) thing to mention is stitch images together which have similar exposure settings. As also mentioned you do not always see via the eyepiece atmospheric disturbances but when you are taking the video clip you will see thet are there.

Neil

[Snaggerman]

Thanks again - some good points here!

I think I'm definately getting some shake, I have a rubbush mount. To try to get over this I set the camera to self-timer, 12 seconds is enough for the mount and camera to settle after I have pressed the shutter, but it appears that the movement of the mirror inside the camera sets up a new wobble! To counteract that I've gone for a faster shutter speed (1/125 I think) and faster film speed (400-800 ASA). Bit grainy but I think it's fast enough to lose the shake....?

I don't understand about increasing the focal length to take shots of portions of the moon - with the camera in place (i.e. without an eyepiece) aren't I fixed with the magnification I get?

Is there any mosiac function within Photoshop CS3? Like automerge? I like the sound of stacking - I'll look into this a bit more.

Thanks again it's great to have somebody to ask!

[Ad Astra]

Hi There,

I can get very nice photos of Luna with single shots on my DSLR. Maybe these tips will help:

1. Use a fairly high ISO setting - this will shorten your exposure time and minimize the effects of distortion from the atmosphere. I find that if I can keep exposures down to 1/10th sec, I have very few problems - the seeing just doesn't change that fast.

2. I try to make sure I'm not trying to shoot over a roof, roadway, or parking lot. All these structures absorb heat during the day, and radiate it away at night, roiling the air directly above them for quite a distance. This seriously contributes to focusing problems.

3. Once I have an exposure I like, I move the focus back a bit, and then, one exposure at a time, I rack the focuser forward again, (very small movements!!!) making a series of exposures. I've tried focusing with masks, but haven't had that much success with it when focusing on Luna. However a series of exposures works very well.

4. I use eyepiece projection -- my camera adapter allows me to insert an eyepiece between the camera and the scope, giving me a higher mag shot, narrower field - and less problems with seeing and distortion.

You can see a couple of nice single exposure shots from my camera & scope by clicking <HERE> (Note that these are thumbnail images, click on the images and you will see them in a better size format - still not the nice full size photo files, but that's all that fits on the web!)

I hope that helps some,

Dan