Focusing mylar filter on A DSLR

Domol (Domenic) · #1 30-10-2012, 05:07 PM

Hi There,
I'm having difficulty focusing my Canon 40d & 400mm with a mylar filter. I get thew image very sharp in live view, but when i zoom in afterwards the sunspots are fuzzy? It it a focus issue, or is it just poor seeing? (can you get poor seeing at 400mm) -
See attachement done 3pm so sun was about 54 degree high. Thanks for your comments

Also, any ideas on seeing the LCD screen is full sunshine.

pluto (Hugh) · #2 30-10-2012, 05:28 PM

If the image is sharp in liveview I wouldn't think that the filter would be the problem. Are you taking these as raws?
Also perhaps you could take a shot of the moon and see if you get the same softness..?
I haven't used mylar film but during the transit I chucked some of the viewing glasses in front of my lens (on a 7D) and those images were reasonably sharp (perhaps a bit sharper than yours but much smaller).

As for seeing the screen, perhaps you could chuck a black cloth/towel over your head and the camera body...?

Larryp (Laurie) · #3 30-10-2012, 05:39 PM

Hi Domenic
You say you are getting good focus in Liveview and then zooming in. If you are focusing and then zooming, you are probably losing your focus. You should focus at the focal length at which you want to take the image.

stardust steve (Steve) · #4 30-10-2012, 05:39 PM

A good way to check live view when focusing, is to drape a large tea towel over your camera and head. This shades the screen and your eyes and makes focusing a lot easier.
When i check focus, i zoom in to the sunspot (10x) in live view. That makes it a bit easier.
Also some pre processing in registax with wavelet adjustments and then some more later in PS with the sharpening section really help those sunpots and detail to show when zoomed in.
This is just what i do and it works ok for me.
Hope it helps and if you find a better way, let me know lol

Edit- i reckon seeing has a fair bit to do with it also.

Moon (James) · #5 30-10-2012, 06:47 PM

Is the mirror in the camera locked up the whole time? If not, it could be a vibration. What is the exposure duration?

bojan · #6 30-10-2012, 07:27 PM

I think Domenic wanted to say he was zooming in the taken picture on the monitor screen later.

Yes, it is the seeing - there are a lot of turbulences during a day.
Live image on the small camera screen may seem a lot sharper, because our eyes are "processing" turbulent image, so it appears sharper than it actually is.

Domol (Domenic) · #7 30-10-2012, 08:16 PM

Thanks for the feedback guys
Yes, i was zooming in on the PC afterwards to analyse
The black drape is an excellent idea and i'll go and snap the moon right now! to compare
thanks

Domol (Domenic) · #8 30-10-2012, 08:18 PM

oh, and I was using 1/5000 on a manfrotto tripod, so hopefully it's not vibration??

ZeroID (Brent) · #9 31-10-2012, 10:53 AM

I'm getting the same thing, looks good on screen but lacks detail in the pic, almost out of focus and fuzzy. ISO200 and about 1/500 through an 80mm f5 Achro Scope.
It is not the scope because I got surprisingly excellent results on Lagoon and Trifid with a CLS filter.
On screen I can see sunsppots and the edge distortion\detail bu afterwards it is just a dark blob inside a not so dark blob.
Focus\wavelength ??

sil (Steve) · #10 01-11-2012, 04:00 PM

As well as the explanations provided there can also be vibration contributing to the softness. If you're on tripod you shouldn't have any vibration reduction enabled (but try with it on/off and see whats sharpest for you).

When the shutter is triggered and the mirror flips the whole camera can wobble. It's not much but anyone will tell you the longer the focal length (ie more magnification) the more exagerated the tiniest movement becomes. If you're near an airport try taking a 10sec+ exposure of a plane (trigger the shutter while the plane is in the field of view), then take a very close look at the solid line trail of the plane...is the start of trail a little bit blobbier than the rest of the line, does the line exhibit a reducing sine wave effect? You can use distant traffic or any fast moving light that will cause a solid line across most of the sensor within a few seconds...long enough to see the wobble start and then settle. Sometimes you can even see it watching a bright star through the lens and see it bounce up and down when the shutter is triggered (triggered, not pressed). Using the timer won't help at all.

If the lens is a zoom lens you can also get zoom creep from the weight of the glass. So you zoom the lens all the way out to maximum and tilt your camera upwards and gravity will help the lens to creep back towards the camera slightly. So you might get sharp focus but when you let go of the setup and trigger your shot the lens may have crept a little and as a result lost focus.

Also depends on the lens itself. The lens and camera may need micro adjustments to gain optimal sharpness. Sharpness won't be perfectly even across the sensor either. Likewise the f-stop value you shoot at will change the sharpness (generally lenses are sharper several stops down from their fastest f-stop). You'll just need to test your set up and find out where your lens/camera will give you the sharpest result.

Again, as well as the mentioned seeing conditions as well from others. No one factor will be causing it. Your shot is pretty typical from what I get, then when I stack and can get really nice sharp sunspots.

steve000 (Steve) · #11 01-11-2012, 05:03 PM

I had similar, I found auto focus was close. If its a 400mm telescope just zoom in to the sunspot as much as you can then adjust focus. Works for me with similar setup, 500mm refractor and 400mm lens

Domol (Domenic) · #12 01-11-2012, 05:52 PM

I can understand that Vibration could be a factor, but wouldn't the sun edge be fuzzy too?

[
QUOTE=sil;910402]As well as the explanations provided there can also be vibration contributing to the softness. If you're on tripod you shouldn't have any vibration reduction enabled (but try with it on/off and see whats sharpest for you).

When the shutter is triggered and the mirror flips the whole camera can wobble. It's not much but anyone will tell you the longer the focal length (ie more magnification) the more exagerated the tiniest movement becomes. If you're near an airport try taking a 10sec+ exposure of a plane (trigger the shutter while the plane is in the field of view), then take a very close look at the solid line trail of the plane...is the start of trail a little bit blobbier than the rest of the line, does the line exhibit a reducing sine wave effect? You can use distant traffic or any fast moving light that will cause a solid line across most of the sensor within a few seconds...long enough to see the wobble start and then settle. Sometimes you can even see it watching a bright star through the lens and see it bounce up and down when the shutter is triggered (triggered, not pressed). Using the timer won't help at all.

If the lens is a zoom lens you can also get zoom creep from the weight of the glass. So you zoom the lens all the way out to maximum and tilt your camera upwards and gravity will help the lens to creep back towards the camera slightly. So you might get sharp focus but when you let go of the setup and trigger your shot the lens may have crept a little and as a result lost focus.

Also depends on the lens itself. The lens and camera may need micro adjustments to gain optimal sharpness. Sharpness won't be perfectly even across the sensor either. Likewise the f-stop value you shoot at will change the sharpness (generally lenses are sharper several stops down from their fastest f-stop). You'll just need to test your set up and find out where your lens/camera will give you the sharpest result.

Again, as well as the mentioned seeing conditions as well from others. No one factor will be causing it. Your shot is pretty typical from what I get, then when I stack and can get really nice sharp sunspots.[/QUOTE]

sil (Steve) · #13 02-11-2012, 01:38 PM

Quote:

Originally Posted by Domol

I can understand that Vibration could be a factor, but wouldn't the sun edge be fuzzy too?

and it sure is.

If you're expecting razor sharp images like what other people post then forget it. What you've posted is pretty typical for a single out of the camera shot. A little softer all over than is possible, but pretty typical. The softness could be any or all of the factors already listed in this thread. Nice sharp photos that make us go "wow" are to be gotten by image stacking and processing to bring out the sharpness.

Do a test: pin a page of sharp black text on white paper (eg a page from a magazine) to a wall. set up your camera far back with the same lens and shoot the page. now take a look at how sharp the text looks on your computer screen compared to the page of text itself.

Many factors could contribute to varying degrees (as have been listed). It'll be up to you to work on the ones you can influence/control so that those at least are minimised.