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Advice on focusing on the moon???

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#1 kesselrun

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Posted 19 January 2013 - 11:26 AM

Hi everyone, this is my first post here. I've been using a DSLR with a 3X barlow on a 5 inch reflector. When I focus on the moon, during the day, like today, the image I see through the camera isn't what the final shot looks like.
Through the viewfinder the image is nice and sharp but when I take a shot it's quite blurry. The camera is set to 800 iso 1/200th of a sec, so there's no chance the moon is moving during the exposure or is there?
I've attached an example.
Cheers

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#2 kesselrun

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Posted 19 January 2013 - 11:32 AM

Any help would be great?
Thanks

#3 Cliff Hipsher

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Posted 19 January 2013 - 11:53 AM

What camera? Back in the day before I got into astronomy I had 35mm SLRs. Because I had slight myopia I could not trust my eye to focus a shot. I had to use the camera's focus screen.

Some DSLRs have LDC screens. Canons have a function called Live View. Try using either a Hartman or a Bahtinov mask.

#4 DavidC

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Posted 19 January 2013 - 11:53 AM

I'm not sure, you really need to ask this question in the DSLR imaging section.
David

#5 DavidC

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Posted 19 January 2013 - 11:57 AM

Second thought, maybe that 3X barlow is too much magnification for that 5 inch reflector, that might be the reason for the soft image.

#6 NeilMac

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Posted 19 January 2013 - 12:04 PM

Use Live View to fine tune the focus.
Other then that, make sure you are not experiencing air turbulence thats distorting the image.

#7 Jon Isaacs

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Posted 19 January 2013 - 12:56 PM

Through the viewfinder the image is nice and sharp but when I take a shot it's quite blurry. The camera is set to 800 iso 1/200th of a sec, so there's no chance the moon is moving during the exposure or is there?



I am not sure the focal length of your scope but with a 3x Barlow, it's probably operating at a focal length of between 2000mm -3000mm, that takes a stable mount and just pushing the button or even the bump of the camera mirror as it moves out of the way can be enough to cause a blurred image. If you are not using a remote shutter control, you might try using a 10 second delay.

Jon

#8 jgraham

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Posted 19 January 2013 - 01:11 PM

It is common practice to set the focus on a bright star using a focusing mask (Hartmann or Bahtinov) then slew to the moon.

#9 kesselrun

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Posted 19 January 2013 - 01:21 PM

Great, thanks everyone.

I have a Canon 350D, so no live view available. I already use a 10 second delay, so I suspect the bump doesn't help.

A better, less powerful barlow might be in order too?

Geoff

#10 Mark9473

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Posted 19 January 2013 - 02:54 PM

Your image actually looks like it's not focussed. Are you sure the diopter setting of your viewfinder is correctly set for your eye? You could also mount a magnifying loupe on the viewfinder.

You are using manual focus, right? AF will often miss a bit. MF is difficult to get right without live view but is still the better choice IMO.

Give it a try without the barlow just to make sure.

#11 csrlice12

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Posted 19 January 2013 - 03:01 PM

Turn the twirly knobs next to the focuser. :lol:

Sorry. Couldn't help myself....

#12 Cliff Hipsher

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Posted 19 January 2013 - 03:34 PM

Second thought, maybe that 3X barlow is too much magnification for that 5 inch reflector, that might be the reason for the soft image.


Nice catch. Not sure how the OPs camera is, but with the typical web cam you get about the same magnification as a 12mm EP will give you.

However, with a 3x Barlow his image should not be a "full" moon. A section maybe, but not the whole thing...

I'd really like to know what brand and model this 5" scope is. :question:

#13 Pharquart

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Posted 19 January 2013 - 05:24 PM

I already use a 10 second delay, so I suspect the bump doesn't help.


The delay helps the imaging mount settle down before the shutter opens. It's a requirement if you're not using a remote trigger. However, there's another source of vibration that can get into astro images: the reflex mirror popping up. An SLR (digital or film) has a mirror that reflects the light from the lens up into the viewfinder. Right before an exposure, the mirror pulls out the way to open up the light path to the imaging plane. It's the "click-click" that you hear when you take a shot. That motion can cause enough vibration to blur your shot at extremely high magnifications like through a telescope.

On my Canon 1000D, there's a setting called "mirror lockup" that pulls the mirror out of the way on the first press of the trigger, then actually takes the picture on the second press. I pull the mirror, wait 2 seconds for vibrations to die down, then take the picture. I've only used it with a remote (on BULB exposure setting), with 1 second or longer exposures, but I think it would work with short exposures as well. You'll have to experiment.

Brian

#14 jrcrilly

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Posted 19 January 2013 - 05:38 PM

You can't rely on viewfinder focus for several reasons. For one, as has been mentioned, that is adjustable and may or may not be properly adjusted to agree with the chip. For another, it simply isn't as precise as you would require. The primary reason, though, is that your eye can accommodate a range of focus positions so even when it's out of focus your eye can correct it to appear in focus - but the camera chip cannot.

A focus mask can compensate for the above to some extent - but a certain method is to look at what the chip is seeing. Short test shots are the way to go. Bear in mind - dedicated astro cameras have neither viewfinders nor "live view" but they are easy to focus via test shots.

Shutter shock and/or mirror slap are possible, but as your focus method can't be trusted, and as the shot appears out of focus, I'd fix that first.

#15 kesselrun

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Posted 19 January 2013 - 08:12 PM

Just a little extra info:

Canon 350D set to manual and using 10 sec delay
Prime Focus
Budget Tasco 114mm Mirror Reflector-Laser Collimated
3X Budget barlow.

Thanks again for all advice.

#16 cavefrog

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Posted 19 January 2013 - 08:36 PM

You can't rely on viewfinder focus for several reasons. For one, as has been mentioned, that is adjustable and may or may not be properly adjusted to agree with the chip. For another, it simply isn't as precise as you would require. The primary reason, though, is that your eye can accommodate a range of focus positions so even when it's out of focus your eye can correct it to appear in focus - but the camera chip cannot.

A focus mask can compensate for the above to some extent - but a certain method is to look at what the chip is seeing. Short test shots are the way to go. Bear in mind - dedicated astro cameras have neither viewfinders nor "live view" but they are easy to focus via test shots.

Shutter shock and/or mirror slap are possible, but as your focus method can't be trusted, and as the shot appears out of focus, I'd fix that first.


I agree with John... your picture appears out of focus. try focusing on the near side of what appears to be focused, and take several pictures while moving the focus towards the far side of focus. you will probably find your best focal point in there somewhere.

Theo

#17 cavefrog

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Posted 19 January 2013 - 08:40 PM

and wecome to CN!

#18 drewp

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Posted 20 January 2013 - 01:59 PM

It is common practice to set the focus on a bright star using a focusing mask (Hartmann or Bahtinov) then slew to the moon.

i used a mask with my old 20D for the same reason. could never get the quality of focus threw the viewfinder and screen views were not much help nor was the method of taking multiple shots of the same subject adjusting focus for each. the focus mask does work and gives the most reliable repeatable results with fewest resulting gray hairs

#19 newtoskies

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Posted 20 January 2013 - 02:04 PM

Does look like a focus issue. I was thinking of taking a daytime pic of the moon the other day. May have to give it a go. Love the deep blue in your image.

#20 Turf1

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Posted 20 January 2013 - 02:21 PM

Daytime photo is one I have not tried, I am new to this with my DSLR with primary photos. I use my Nikon D50, it does NOT have live view. I have a hard time focusing thru the "view" finder to get it right, so I take test shots with small adjustments till it is ok with me.As others have said, and I agree, I think the fucus you have needs just a little tweeking and it would be great!This shot was taken just using delayed shutter release,yes its not perfect, but the fun is in the trying right? :)

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#21 kesselrun

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Posted 29 January 2013 - 02:16 PM

Oopss double post, sorry.

#22 kesselrun

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Posted 29 January 2013 - 02:21 PM

Yes Turf1, thanks for the reply, it's good to know somebody was/is in the same boat.
It's great to actually receive positive feedback on a forum!!!
Good work CN!!

#23 michael hester

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Posted 29 January 2013 - 02:31 PM

Most of the new Canon DSLRs have a live view zoom mode, you can try focusing in that mode. The view finder won't tell you if you're in focus unless you use a lens rather than your telescope.

A 5 inch should be capable of excellent detail on the moon.






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