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11-08-2009, 08:57 AM   #1
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Does the istD have Amplifier Glow on long exposures

Background: I'd been using a filterless Pentax K110D for astrophotography for a few years. It served me well, especially on red nebulas where an un-modified DSLR works poorly. As mentioned in another thread I stepped on a cable in the dark and broke the video/USB connector on the side of the camera. The camera still works but it can not be used with an external monitor. I had an istD available and it became my astro camera. It has a few advantages:

1. Connector is not broken so I can use a video monitor to focus.
2. Stronger connector design.
3. Better color on stars since it has its internal filter.
4. It works with Pentax Remote Assistant so I can focus on a computer as well.

Problem: I keep getting a red glow in the upper left corner. At first I assumed it was my fault, but the glow appeared every time I used the istD. I have not heard mention of a Pentax having, "Amp Glow." This is a problem with early Canons (and other brands) where a heat source such as the signal amplifier causes noise in one corner of the image. This only occurs with long exposures where heat results in noise. The glow can not be removed with flat fields since flat exposures are short. The images I take use in camera Noise Reduction (AKA dark fields). I know, don't get into separate darks.

Has anyone on the forum observed Amp Glow on an istD? Are there other possible causes for this symptom. Again, I don't have this glow with my K110D or K100D cameras. If I can't solve this I may have to go back to the K110D and re-learn to focus on the tiny LCD monitor. It is so much easier to focus with a 13 inch TV as a monitor!

The example is a galaxy cluster around NGC 7619. Fifteen exposures of 2 minutes stacked with Images Plus. There are about 8 galaxies in the image, the "faint fuzzies" are hard to see with the red glow.

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11-08-2009, 04:16 PM   #2
Ash
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This appears to me as amplified flare.
I've had many long exposure night shots spoilt from it.
Same colour and characteristics.
Where some light is streaming ever so slightly across the lens around where the camera is placed, there is going to be this phenomenon. Shielding the front element from any surrounding light sources may help avoid this.
11-08-2009, 05:16 PM   #3
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QuoteOriginally posted by Ash Quote
This appears to me as amplified flare.
I've had many long exposure night shots spoilt from it.
Same colour and characteristics.
Where some light is streaming ever so slightly across the lens around where the camera is placed, there is going to be this phenomenon. Shielding the front element from any surrounding light sources may help avoid this.
The front element, in the case of this telescope the corrector plate, has a shield that extends about 15 inches past it. It is a flat black tube 8 inches in diameter, almost as large as the telescope itself.

I'm currently imaging the same object in the same orientation using a K110D. I looked over the first 8 frames and did not see red glow in the corner. At the end of the evening I should have results that show the istD has a problem the K110D does not. I'm wondering if it with my particular istD which otherwise has worked fine many years.
11-08-2009, 05:23 PM   #4
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Not sure.
I've had the purple hot spots come up on shots taken with a *ist D, K10D and K20D.
Once I'd taken the camera to a lightless environment around it, they weren't there anymore.
Would be interesting to hear what comes of your experience.

11-11-2009, 07:08 PM   #5
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I had the results from the K110D a few days ago and forgot to post them. This is the same galaxy cluster, same telescope, same exposure time (2 minutes). It is 36 exposures but I did stack a smaller number with similar results.

There is a slight glow in the upper left, but so little I can see why I never noticed it before. This is a keeper, I added a larger version to my web site.

Bottom line is my istD appears to have serious "amp glow" in the upper left. I have not heard from anyone that they experienced the same thing so do not know if all istDs suffer this malady. The K110D was not "that hard" to focus on the LCD since I recently started using a Bahtinov mask. I will miss my monitor but I'm going to cease using the istD for astrophotos. One important advantage of the monitor was to focus when aimed high overhead which is needed for some jobs like imaging the International Space Station. I may use a K100D for those nights.
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11-11-2009, 07:15 PM   #6
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Definitely amp glow, I see similar but smaller on my K10.

@Ash: When you took the camera to a darker site was the temperature cooler? Cooling a sensor (think winter) is the best thing you can do for both amp glow and noise. Although I should mention that amp glow is self generating due to the energy consumed by the circuit - you can only lessen it in cold climates not get rid of it.
11-11-2009, 07:35 PM   #7
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QuoteOriginally posted by LeoTaylor Quote
I had the results from the K110D a few days ago and forgot to post them. This is the same galaxy cluster, same telescope, same exposure time (2 minutes). It is 36 exposures but I did stack a smaller number with similar results.

There is a slight glow in the upper left, but so little I can see why I never noticed it before. This is a keeper, I added a larger version to my web site.

Bottom line is my istD appears to have serious "amp glow" in the upper left. I have not heard from anyone that they experienced the same thing so do not know if all istDs suffer this malady. The K110D was not "that hard" to focus on the LCD since I recently started using a Bahtinov mask. I will miss my monitor but I'm going to cease using the istD for astrophotos. One important advantage of the monitor was to focus when aimed high overhead which is needed for some jobs like imaging the International Space Station. I may use a K100D for those nights.
I have a D but take very few long exposures but I do remember some amp glow (same area) in some not-too-long exposures w/ DFS off when I first got the camera...
OK a quick 30sec check w/ nr off produced a good start to a glow in the upper left....

Last edited by jeffkrol; 11-11-2009 at 07:40 PM.
11-11-2009, 08:18 PM   #8
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QuoteOriginally posted by JackBak Quote
Definitely amp glow, I see similar but smaller on my K10.

@Ash: When you took the camera to a darker site was the temperature cooler? Cooling a sensor (think winter) is the best thing you can do for both amp glow and noise. Although I should mention that amp glow is self generating due to the energy consumed by the circuit - you can only lessen it in cold climates not get rid of it.
Cooler temperatures certainly help, but where I got flare was no cooler in temperature than where I didn't get flare.

The biggest issue for me was avoiding cross lighting not being shielded by the lens hood, particularly horizontal light when in landscape orientation or vertical light in portrait orientation.

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