Obligitory Moon Shot

Obligitory Moon Shot · 06:07 PM

I think I found the sweet spot for the Sigma 100-300 f4.0 EXDG with the matching 1.4x TC.

Pentax K10D ,Sigma 100-300mm f/4 APO EX DG 1/15s f/11.0 at 300.0mm iso100 w/Sigma 1.4X EX DG Tele Converter

Peter Zack · 10-22-2007, 06:16 PM

Good shot. looks quite sharp and detailed. I'd say you got the shutter speed right on. Sweetspot? 300mm or f11? Or do you mean you want to fire the thing off at the moon sometimes????

zoomzoomfan · 10-23-2007, 12:53 AM

Awesome shot. I've got a Pentax FA 100-300 F4 that I've been trying to use for moonshots, with little luck. Then again, I wasn't making any serious efforts.

Question: Was any post processing done?

I think this shot might have convinced me to spend a few bucks on a TC.

ChrisA · 10-23-2007, 01:45 AM

Originally posted by Peter Zack

I'd say you got the shutter speed right on.

1/15s is really slower than I'd dare to use at this focal length. The moon moves surprisingly fast across the sky and unless you keep the shutter speeds short you risk movement blur.

I think this shot looks a bit over exposed, myself. It would have been fine with a stop, maybe 1.5 stops less, and may well have been just a touch sharper as well.

roscot · 10-23-2007, 05:01 AM

Thanks for the comments everyone.

Peter: The lens is as big as a cannon, so shooting it off at the moon isn't a bad idea (LOL). What I've been attempting to do is find the best aperture to use with the matching TC. I hadn't been pleased with the overall sharpness in previous shots at wider openings. So I now know how far to stop down to maximize sharpness with the TC. On it's own, the lens is very good at f4.0, better at f5.6 and a razor at f8.0. What really pleased me is that even though this was a high contrast image, there was very little CA. Just a touch of cyan, easily removed in ACR.

ZoomZoomFan: I shoot in RAW so yes there was processing. Opened in ACR, made some basic adjustments to WB, exposure, clarity, and CA. Converted to b&w in CS3 using the B&W adjustment layer, and added a bit of contrast and sharpening.

Chris: Thanks for the C & C. Actually the shot was about 1/2 stop under exposed. I compensated in ACR, I also added contrast when I converted to B&W. I probably went a tad to far, but I still see plenty of detail. I agree, about this copy of the image being slightly soft, but, I think that happened in the downsizing and uploading to the web. The original is very sharp indeed.

ChrisA · 10-23-2007, 05:25 AM

Originally posted by roscot

I agree, about this copy of the image being slightly soft, but, I think that happened in the downsizing and uploading to the web. The original is very sharp indeed.

Curious. Resizing an image smaller should normally make it look sharper, not less sharp. It's looking to me like you've reduced it to a little more than half its original size.

It would be interesting to see a version of the un-resized original if you wouldn't mind? On the K10D, at 300mm x 1.4 = 420mm, I'm estimating the diameter of the moon at about 610 pixels, which is easily small enough to post here, even with a small border.

(My moon shots were all taken with a 400mm lens, and un-resized occupy about 580 pixels.)

Incidentally, I didn't say the image you posted looks soft; I think it's pretty good. I was just saying that you risk movement blur with long exposures.

Peter Zack · 10-23-2007, 05:59 AM

ChrisA, I'd agree that this seems like a very slow speed and my attempts have been at much higher speeds but given the results, I'd say this is much better than most I've seen. Marc posted the best shot a few days ago but I can't remember what speed he was at. I need to go and try this again myself and see what works. I suspect I need to weigh the tripod down and make it even more rigid as I am not getting the same clarity as others.

roscot · 10-23-2007, 06:02 AM

Originally posted by ChrisA

Incidentally, I didn't say the image you posted looks soft; I think it's pretty good. I was just saying that you risk movement blur with long exposures.

you're probably right about the movement. I don't shoot the moon enough to know.

I did fail to mention this shot is also cropped to about 3000 x 2400 pixels.

ChrisA · 10-23-2007, 06:04 AM

Follow up:

Out of interest, I did some calculations which may be of interest:

Based on Roscot's 420mm lens/TC combo, the angle of view on the K10D will be equivalent to 630mm on 35mm format, which gives a horizontal angle of view of 3.3 degrees.

The moon moves at 0.25 degrees per minute, so assuming that it's all set up to track horizontally across the frame, the K10D's 3872 pixels will take:

3.3/0.25 = 13.2 minutes = 792 seconds to be crossed by the moon.

This equates to 3872/792 = 4.9 pixels per second.

So an exposure of 1/15s amounts to about 1/3 of a pixel. So 1/3 of the light hitting a pixel at the start of the exposure will get smeared into the next pixel by the end of the exposure, thus reducing the contrast.

This is only a "back of an envelope" type of calculation, and of course completely ignores other effects like lens resolution, but it illustrates the need to keep exposures short.

Hope it's of some interest, anyway - and that I've done the sums right. If I have, then 1/15s is probably just about Ok.

ChrisA · 10-23-2007, 06:10 AM

Originally posted by roscot

I don't shoot the moon enough to know.

Don't get me wrong - if this is one of your early attempts it's good. I've had lots of goes and been disappointed more often than not.

For comparison, here's one I took in August with the K10D and a Pentax SMC-A 400mm F5.6:

I don't think the editing is quite optimised yet, but I won't be able to get it much better than this.

roscot · 10-23-2007, 06:11 AM

LOL, Chris, you've gone way over my head. I'll assume you are correct. It is interesting, though. As a layman, I would not think the moon would travel that fast through a camera frame. If I have good weather tonight, I'll try reshooting at a higher ISO/TV. It will be interesting if I can see the difference.

Thanks for doing the math. Time for me to do what I get paid for around here.

ChrisA · 10-23-2007, 06:25 AM

Originally posted by roscot

As a layman, I would not think the moon would travel that fast through a camera frame.

Indeed. I was that layman back in March, when I attempted to shoot the lunar eclipse visible from England back then.

Of course, not much light coming from the moon when it's in shadow. I used exposures of about 3 seconds (trust me - a 15 pixel blur is enough to ruin things).

Result: unmitigated garbage.

Then I did the math, and wished I'd done it before, not after

Syb · 10-24-2007, 02:21 AM

Bump. Chris' calculation is interesting, also considering the large amounts of moonshots that came up recently. Besides: the images are great!

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10-23-2007, 05:25 AM	#6
ChrisA Veteran Member Join Date: Feb 2007 Location: London Posts: 393	Originally posted by roscot I agree, about this copy of the image being slightly soft, but, I think that happened in the downsizing and uploading to the web. The original is very sharp indeed. Curious. Resizing an image smaller should normally make it look sharper, not less sharp. It's looking to me like you've reduced it to a little more than half its original size. It would be interesting to see a version of the un-resized original if you wouldn't mind? On the K10D, at 300mm x 1.4 = 420mm, I'm estimating the diameter of the moon at about 610 pixels, which is easily small enough to post here, even with a small border. (My moon shots were all taken with a 400mm lens, and un-resized occupy about 580 pixels.) Incidentally, I didn't say the image you posted looks soft; I think it's pretty good. I was just saying that you risk movement blur with long exposures. Last edited by ChrisA; 10-23-2007 at 05:32 AM.

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10-22-2007, 06:16 PM	#2
Peter Zack Pentaxian Moderator Emeritus Join Date: May 2007 Location: Edmonton Alberta, Canada Photos: Gallery \| Albums Posts: 10,643	Good shot. looks quite sharp and detailed. I'd say you got the shutter speed right on. Sweetspot? 300mm or f11? Or do you mean you want to fire the thing off at the moon sometimes????

10-23-2007, 12:53 AM	#3
zoomzoomfan Junior Member Join Date: Sep 2007 Location: Vancouver, BC Posts: 47	Awesome shot. I've got a Pentax FA 100-300 F4 that I've been trying to use for moonshots, with little luck. Then again, I wasn't making any serious efforts. Question: Was any post processing done? I think this shot might have convinced me to spend a few bucks on a TC.

10-23-2007, 01:45 AM	#4
ChrisA Veteran Member Join Date: Feb 2007 Location: London Posts: 393	Originally posted by Peter Zack I'd say you got the shutter speed right on. 1/15s is really slower than I'd dare to use at this focal length. The moon moves surprisingly fast across the sky and unless you keep the shutter speeds short you risk movement blur. I think this shot looks a bit over exposed, myself. It would have been fine with a stop, maybe 1.5 stops less, and may well have been just a touch sharper as well.

10-23-2007, 05:01 AM	#5
roscot Veteran Member Join Date: Sep 2006 Location: Virginia Beach VA USA Photos: Gallery Posts: 1,363 Original Poster	Thanks for the comments everyone. Peter: The lens is as big as a cannon, so shooting it off at the moon isn't a bad idea (LOL). What I've been attempting to do is find the best aperture to use with the matching TC. I hadn't been pleased with the overall sharpness in previous shots at wider openings. So I now know how far to stop down to maximize sharpness with the TC. On it's own, the lens is very good at f4.0, better at f5.6 and a razor at f8.0. What really pleased me is that even though this was a high contrast image, there was very little CA. Just a touch of cyan, easily removed in ACR. ZoomZoomFan: I shoot in RAW so yes there was processing. Opened in ACR, made some basic adjustments to WB, exposure, clarity, and CA. Converted to b&w in CS3 using the B&W adjustment layer, and added a bit of contrast and sharpening. Chris: Thanks for the C & C. Actually the shot was about 1/2 stop under exposed. I compensated in ACR, I also added contrast when I converted to B&W. I probably went a tad to far, but I still see plenty of detail. I agree, about this copy of the image being slightly soft, but, I think that happened in the downsizing and uploading to the web. The original is very sharp indeed.

10-23-2007, 05:59 AM	#7
Peter Zack Pentaxian Moderator Emeritus Join Date: May 2007 Location: Edmonton Alberta, Canada Photos: Gallery \| Albums Posts: 10,643	ChrisA, I'd agree that this seems like a very slow speed and my attempts have been at much higher speeds but given the results, I'd say this is much better than most I've seen. Marc posted the best shot a few days ago but I can't remember what speed he was at. I need to go and try this again myself and see what works. I suspect I need to weigh the tripod down and make it even more rigid as I am not getting the same clarity as others.

10-23-2007, 06:02 AM	#8
roscot Veteran Member Join Date: Sep 2006 Location: Virginia Beach VA USA Photos: Gallery Posts: 1,363 Original Poster	Originally posted by ChrisA Incidentally, I didn't say the image you posted looks soft; I think it's pretty good. I was just saying that you risk movement blur with long exposures. you're probably right about the movement. I don't shoot the moon enough to know. I did fail to mention this shot is also cropped to about 3000 x 2400 pixels.

10-23-2007, 06:04 AM	#9
ChrisA Veteran Member Join Date: Feb 2007 Location: London Posts: 393	Follow up: Out of interest, I did some calculations which may be of interest: Based on Roscot's 420mm lens/TC combo, the angle of view on the K10D will be equivalent to 630mm on 35mm format, which gives a horizontal angle of view of 3.3 degrees. The moon moves at 0.25 degrees per minute, so assuming that it's all set up to track horizontally across the frame, the K10D's 3872 pixels will take: 3.3/0.25 = 13.2 minutes = 792 seconds to be crossed by the moon. This equates to 3872/792 = 4.9 pixels per second. So an exposure of 1/15s amounts to about 1/3 of a pixel. So 1/3 of the light hitting a pixel at the start of the exposure will get smeared into the next pixel by the end of the exposure, thus reducing the contrast. This is only a "back of an envelope" type of calculation, and of course completely ignores other effects like lens resolution, but it illustrates the need to keep exposures short. Hope it's of some interest, anyway - and that I've done the sums right. If I have, then 1/15s is probably just about Ok.

10-23-2007, 06:10 AM	#10
ChrisA Veteran Member Join Date: Feb 2007 Location: London Posts: 393	Originally posted by roscot I don't shoot the moon enough to know. Don't get me wrong - if this is one of your early attempts it's good. I've had lots of goes and been disappointed more often than not. For comparison, here's one I took in August with the K10D and a Pentax SMC-A 400mm F5.6: I don't think the editing is quite optimised yet, but I won't be able to get it much better than this.

10-23-2007, 06:11 AM	#11
roscot Veteran Member Join Date: Sep 2006 Location: Virginia Beach VA USA Photos: Gallery Posts: 1,363 Original Poster	LOL, Chris, you've gone way over my head. I'll assume you are correct. It is interesting, though. As a layman, I would not think the moon would travel that fast through a camera frame. If I have good weather tonight, I'll try reshooting at a higher ISO/TV. It will be interesting if I can see the difference. Thanks for doing the math. Time for me to do what I get paid for around here.

10-23-2007, 06:25 AM	#12
ChrisA Veteran Member Join Date: Feb 2007 Location: London Posts: 393	Originally posted by roscot As a layman, I would not think the moon would travel that fast through a camera frame. Indeed. I was that layman back in March, when I attempted to shoot the lunar eclipse visible from England back then. Of course, not much light coming from the moon when it's in shadow. I used exposures of about 3 seconds (trust me - a 15 pixel blur is enough to ruin things). Result: unmitigated garbage. Then I did the math, and wished I'd done it before, not after

10-24-2007, 02:21 AM	#13
Syb Veteran Member Join Date: Aug 2007 Location: Near Utrecht, Netherlands Photos: Gallery Posts: 1,221	Bump. Chris' calculation is interesting, also considering the large amounts of moonshots that came up recently. Besides: the images are great!