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Bloated stars with my TEC140/Trius

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#1 PRejto

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Posted 21 September 2014 - 02:07 AM

Is anyone here imaging with a TEC140 or TEC180 (or other APO) using a Trius (or other brand camera with the ICX694 sensor?

 

I'm getting very bloated stars in the blue channel, and bloated stars in Luminance. I'm using focusMax & Baader filters. No matter how well I focus I end up with what looks to be an out of focus blue channel. I've even gone so far as to try creating separate v curves just for the blue filter. The odd thing is that CCDInspector will report rather decent FWHM values for blue.

 

I realize that atmospheric distortion will have a greater impact on blue but I think what I'm seeing is abnormal.

 

If you are using the ICX694 successfully or unsuccessfully with a TEC or other APO I would really appreciate a reply. My gut feeling tells me that this might be due to the increased sensitivity of this sensor perhaps dovetailing with something about the way the TEC scopes may be corrected. I'm particularly curious to know if this kind of issue is seen with different brand APOs, or different brand cameras.

 

The blue channel was taken earlier in the evening just west of the meridian. I took some shorter exposures that have a bit better FWHM which would indicate tracking and or atmospheric contributions. However even those shorter images show the bloat and out of focus look.

 

Many thanks,

 

Peter

 

Image shown at 160% in order  Blue, Green, Red

 

PS Another imager in Australia is having a similar issue with bloated stars on his TEC180/Trius combination. Though it isn't yet confirmed that he sees this in the blue channel only. It is quite obvious in Luminance, however.

Attached Thumbnails

  • Mean blue. BBS- 00000009.jpg
  • Mean green NN.00000006.jpg
  • Mean Red.BBS-00000012.jpg
  • CCDINS-.jpg

Edited by PRejto, 21 September 2014 - 02:08 AM.


#2 Madhatter

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Posted 21 September 2014 - 11:28 AM

I have the same issue with my Atik 428EX and and QHY9M with two borg scopes (77EDII and 71FL) in both blue and luminance channels.  I have found the blue bloating somewhat reduced using an IDAS P2 filter but not eliminated entirely. Ted at Hutech said I would see a dramatic improvement, unfortunately I did not find that to be the case, reduced yes, removed no.

Hope you find this useful.

 

Mike


Edited by Madhatter, 21 September 2014 - 11:29 AM.


#3 Peter in Reno

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Posted 21 September 2014 - 12:25 PM

How are you focusing? Bahtinov mask or auto focusing? I started with Bahtinov mask and I too got a little bloated stars using Bahtinov mask. The next weekend I switched to auto focusing with Sequence Generator Pro and it made a big difference. A few microns off can make the image look a little soft. My camera is QSI660 which uses same CCD as yours.

 

Also, bad seeing can result bloated stars. Wind can do that also. Make sure your environmental conditions were good. One night appeared to have bad seeing at the beginning and my FWHM was in the low 4" and as the night went on, FWHM shrunk down to 2.7".

 

I would look at focusing first.

 

Peter



#4 blueman

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Posted 21 September 2014 - 12:27 PM

Filters, seeing or even the response level for the CCD could cause this. Also, too long of an exposure will bloat stars. This Chip has a shallow well, so maybe you should cut back on the time? I notice that you took 300 & 150 second exposures. Did the 150 sec exposures look the same as the 300 sec?

Blueman


Edited by blueman, 21 September 2014 - 12:30 PM.


#5 Peter in Reno

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Posted 21 September 2014 - 01:09 PM

I have exposed as long as 10 minutes with the same chip using Astrodon RGB filters without issues. The shallow well is compensated by low read noise and high QE according to Kevin Nelson from QSI. I wouldn't worry about it.

 

The following link is an unprocessed 10 minute exposure of NGC6946 with Blue filter under pretty heavy light pollution. I measured FWHM with PixInsight and got 2.48". This was taken with TEC 140 APO mounted on A-P1100GTO mount and auto focused with SGP. My image scale is 0.96"/pixel.

 

https://www.dropbox....rame10.fit?dl=0

 

Final processed NGC6946 results at:

http://peternagy.smu...scopes/Galaxies

 

Peter


Edited by Peter in Reno, 21 September 2014 - 01:13 PM.


#6 PRejto

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Posted 21 September 2014 - 03:12 PM

Mike, Peter, and Blueman,

 

Thanks so much for your responses! I would answer sooner but for the large time shift between the States and OZ.

 

Misery loves company, eh? Seems I am not alone but fortunately there are solutions!

 

I did state in my first post that I use FocusMax to focus (a Microtouch system that has previously worked very well with my KAF8300 ccd camera/TEC140). The CCDInspector results show decent FWHM values over RGB for the evening. The shorter blue images (150 sec vs 300 sec) look similar with the main difference being a less dark background. There appears to be some enlargement of stars that increases with exposure length but not anything that looks out of focus. Applying any DDP or non-linear stretch reveals the halo/blur. A post (on this same topic at IceInSpace) indicated that CCDIS probably only looks at the brighter portions of the measured stars when measuring FWHM and that the halo/out of focus look is generated when there is any stretching.

 

I found a chart on the TEC140 lens indicated that it is corrected from 436-1000 nm. The Baader blue filter transmits to ca 380 nm, where the Astrodon looks to cut right at 400 nm. The Hutech IDAS LP Filter cuts ca at 410 nm.

 

Peter, many thanks for posting the blue frame. It sure looks better than what I achieve when stretched. Perhaps it's the Astrodon filter but I suppose one cannot be certain that it isn't something else inherent to the two different cameras such as the CCD chamber covering or the camera electronics.

 

Tonight, if clear, I will use my Hutech in front of the color filters. Perhaps my experience will echo Mike's with some improvement.

 

Anyone out there with a Trius on the TEC140?

 

Thanks for all the help!

 

Peter

 

PS: This photo shows a recent result. Luminance was with the G2-8300 on the TEC180, and RGB with the Trius on the TEC140 - captured simultaneously in 1 hour total time. The blue halos are obvious. The luminance image from the G2-8300 camera has very nice resolution, but adding color from the Trius produces fat not very nice stars.

 

http://www.pbase.com...image/157414303

Attached Thumbnails

  • APO 140 color tests.jpg
  • Baader-LRGB Transmission.gif
  • AstrodonG2ESeriesScansforWeb.jpg
  • Hutech IDAS Spectral Response.gif

Edited by PRejto, 21 September 2014 - 03:31 PM.


#7 Konihlav

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Posted 21 September 2014 - 04:02 PM

PRejto:

 

http://blog.astrofot...avelpech/?p=552

 

or

 

http://blog.astrofot...s= Baader UV/IR

 

:)



#8 David Rosenthal

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Posted 21 September 2014 - 06:30 PM

I use Astrodon Gen II E series filters with my Trius SX694 on a FSQ-106ED and am not seeing any bloating in any channels.  Let me know if you want to see any FITS files, unprocessed or otherwise.  I have raw Iris data from last month.  PM me if you want to see anything.



#9 PRejto

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Posted 21 September 2014 - 07:12 PM

Pavel and David,

 

Thanks so much for your answers!

 

It does seem that maybe Astrodon blue might be the answer with now two imagers reporting OK results with the ICX694. My mistake might be with the Baader filter that only starts cutting from about 380 nm.

 

But, Pavel, I noted in your second link a not so nice comment about the Astrodon blue as transmitting too much UV at 400 nm. Is that still your opinion?

 

Edit: I looked again at one of your articles and read your comment about the Baader UV-IR cut filter. I take it that you are still convinced that it helped with the blue star size? I also looked at the Baader Fringe Killer. It seems to do a similar job to the UV-IR cut but begins cutting quite a bit more aggressively. Perhaps that would be the ticket for the TEC refractors.

 

 

What I really want is a blue filter that cuts around 420-430 nm. I really would prefer not to put the IDAS in front of the G and R channels, though it might provide a quick answer to my problems. Since I'm not collecting luminance from the TEC140 it isn't an issue.

 

Many thanks,

 

Peter

 

Edit: after reading Blueman's comment below I went and compared Peter's sub to the final processed image. I have to agree with him about the blue stars still looking rather large


Edited by PRejto, 22 September 2014 - 01:04 AM.


#10 Lynn K

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Posted 21 September 2014 - 08:50 PM

Hi Peter, I have had a Trius Sx-694 for since last Sept.  I mostly have used it on a C11 with Hyperstar.  I have used twice with my TMB130ss.   When I use the TMB, I use a focal reducer and I was using a Televue 0.8x reducer /flattener at f5.6.   I imaged M8 and M17 using 180 sec Lums  and 90 sec. RGB.  All binned 1x1.  I just examined the combined Lums, reds, greens and blues.   And the star size and shape are very similar in all.

 

I use Astronomik LRGB filters.

 

I see post on Yahoo of imagers using the Trius SX-694 and this is the 1st I have heard of this issue.

 

The only issue I have had with the camera is that I had to collimate the front of the camera to the chip.

 

Sorry, I am not much help, but that is my experience so far.

 

Lynn K.



#11 blueman

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Posted 21 September 2014 - 10:38 PM

I have exposed as long as 10 minutes with the same chip using Astrodon RGB filters without issues. The shallow well is compensated by low read noise and high QE according to Kevin Nelson from QSI. I wouldn't worry about it.

 

The following link is an unprocessed 10 minute exposure of NGC6946 with Blue filter under pretty heavy light pollution. I measured FWHM with PixInsight and got 2.48". This was taken with TEC 140 APO mounted on A-P1100GTO mount and auto focused with SGP. My image scale is 0.96"/pixel.

 

https://www.dropbox....rame10.fit?dl=0

 

Final processed NGC6946 results at:

http://peternagy.smu...scopes/Galaxies

 

Peter

Your blue stars are really bloated in that image. They have a huge blue radius. You seem to that the same problem the OP is talking about.

Blueman



#12 PRejto

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Posted 21 September 2014 - 10:58 PM

Hi Peter, I have had a Trius Sx-694 for since last Sept.  I mostly have used it on a C11 with Hyperstar.  I have used twice with my TMB130ss.   When I use the TMB, I use a focal reducer and I was using a Televue 0.8x reducer /flattener at f5.6.   I imaged M8 and M17 using 180 sec Lums  and 90 sec. RGB.  All binned 1x1.  I just examined the combined Lums, reds, greens and blues.   And the star size and shape are very similar in all.

 

I use Astronomik LRGB filters.

 

I see post on Yahoo of imagers using the Trius SX-694 and this is the 1st I have heard of this issue.

 

The only issue I have had with the camera is that I had to collimate the front of the camera to the chip.

 

Sorry, I am not much help, but that is my experience so far.

 

Lynn K.

Thanks Lynn!

 

Is there any possibility of seeing those two photos?

 

Peter



#13 PRejto

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Posted 21 September 2014 - 11:04 PM

Filters, seeing or even the response level for the CCD could cause this. Also, too long of an exposure will bloat stars. This Chip has a shallow well, so maybe you should cut back on the time? I notice that you took 300 & 150 second exposures. Did the 150 sec exposures look the same as the 300 sec?

Blueman

 

Thanks for your two posts!

 

I notice that you are using a KAF8300 chip camera with the TEC140 and I assume you do not have this problem. Nor did I with my G2-8300 (Moravian). It seems to be an ICX694 issue with this refractor (and others based on 1 post here). I hope finding the right cut filter will possibly resolve the issue!

 

Peter



#14 blueman

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Posted 22 September 2014 - 12:16 AM

 

Filters, seeing or even the response level for the CCD could cause this. Also, too long of an exposure will bloat stars. This Chip has a shallow well, so maybe you should cut back on the time? I notice that you took 300 & 150 second exposures. Did the 150 sec exposures look the same as the 300 sec?

Blueman

 

Thanks for your two posts!

 

I notice that you are using a KAF8300 chip camera with the TEC140 and I assume you do not have this problem. Nor did I with my G2-8300 (Moravian). It seems to be an ICX694 issue with this refractor (and others based on 1 post here). I hope finding the right cut filter will possibly resolve the issue!

 

Peter

 

Hi,

Yes, I use the TEC-140 with an AP reducer for f 5.4 and the ML8300 and Astrondon Gen 2 filters. I do not see the bloated stars with this setup. However, poor conditions can certainly can any one of the filtered subs to be bloated. Sometimes Red will have that effect, yet Blue will be fine. Green is the least likely to be effected by conditions and Blue is not normally effected.

The 8300 chip is also shallow welled, but at 25,000 it is still 10,000 deeper than the chip being discussed.

Do you focus for each filter? If so then I would try experimenting with exposure times for each filter.

Blueman

Blueman



#15 Konihlav

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Posted 22 September 2014 - 02:54 AM


about the Astrodon blue as transmitting too much UV at 400 nm. Is that still your opinion?

 

yes it is. The Astrodon filters are the best money can buy in every aspect, except of one use-case and that is use with DSLR lenses or refractors (especially fast refractors suffer from this problem even more) with not perfect correction in blue color - but that is obvious problem for any refracting optics, except of pricey Takahashi FSQ-106 that has really zero CA. But if Don (I told him this already) makes another Blue filter shifted more towards higher wavelengths then the Tru Balance effect would be diminished... but for all kind of reflectors the Blue and Luminance filters are great.

 

 

 


I really would prefer not to put the IDAS in front of the G and R channels, though it might provide a quick answer to my problems. Since I'm not collecting luminance from the TEC140 it isn't an issue.

 

yes it might provide a quick answer to your problem as well as putting the cheap (#2459210A) Baader UV/IR cut 420-680nm filter there instead of the (more expensive) IDAS LPS-P2 or whatever...

 

the transmittance of the cheap Baader is very high like 98% (from what I remember I have measured on a spectroscope) or even better so you do not loose so much light for your G and R channels.

 

the last option - to find a blue filter passing after 420-430nm I doubt such one exists, but I am a human too (can make mistakes).

 



#16 Konihlav

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Posted 22 September 2014 - 03:31 AM

The 8300 chip is also shallow welled, but at 25,000 it is still 10,000 deeper than the chip being discussed.

 

???

Floyd, please, why (again) you put something totally irrelevant to this topic? And a case that you obviously do not understand (still) ? This debate is not about a flame war between of users of particular cameras (or chips) saying 100% time the same story over and over again - mine is best (because I purchased XXX then XXX is best and your YYY is a ...?). Why again you say something totally irrelevant and moreover "wrong" ? In case someone like to know the answer on this then - it is perfectly OK that Floyd's beloved chip (because didn't have the chance to compare with other and you know, first love is a big one) has say 25,500e- well depth and the other small chip has only about 16,800e- full well depth (based on how the camera maker sets the gain of ADC) because his cam has 5.4um pixels and my cam has 4.54um pixels which squared and compared against gives ratio 1:1.41 (41% bigger surface area of larger pixel cam) and if you multiply 1.41 * 16,800e- you get roughly same number... that's one case. Moreover camera with much lower readout noise allows you to take more subs of shorter duration and for this you do not need a big full well as you do not have to shoot for very long time (long subs) in order to overcome readout noise like with that other camera... and in this favor the other tiny sony camera wins. Lot of people have saturated stars after 60 seconds shooting Luminance with that low full-well depth sony chip. But full well depth is the least important parameter of CCD camera. Every other parameter is much more important.

 

I appreciate if you could stop this and rather tell things only from experience that could actually help others.

 

But your comment on focusing each filter separately is 100% valid! I hope Peter does so...



#17 David Rosenthal

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Posted 22 September 2014 - 07:26 AM

 

about the Astrodon blue as transmitting too much UV at 400 nm. Is that still your opinion?

 

yes it is. The Astrodon filters are the best money can buy in every aspect, except of one use-case and that is use with DSLR lenses or refractors (especially fast refractors suffer from this problem even more) with not perfect correction in blue color - but that is obvious problem for any refracting optics, except of pricey Takahashi FSQ-106 that has really zero CA. But if Don (I told him this already) makes another Blue filter shifted more towards higher wavelengths then the Tru Balance effect would be diminished... but for all kind of reflectors the Blue and Luminance filters are great.

I can agree with also.  I have used Baader LRGB, then Astronomik LRGB, both sets suffered from extreme haloing/reflections along with bloating unless I used an additional IR Cut Filter to help with the bloat.  I switched to AstroDon and have had zero issues since.  My last refractor was the Borg 125SD, which has w wonderfully corrected Pentax optical set, which caused very little blur bloat.  I now use the "pricey Takahashi FSQ-106 that has really zero CA" :) and that very slight issue is gone.  FSQ + TrueBalance = Perfection !



#18 Peter in Reno

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Posted 22 September 2014 - 09:35 AM

Thanks for looking closely at my images.

 

If you are referring to my processed images about blue halos, the first two images have Luminance and pseudo-Luminance added to RGB and show blue halos. But the third image is just RGB and IMHO blue halos are much smaller. That's why I uploaded three different processed images of the same galaxy for others to evaluate. If you blink between the first three images, you can see the blue halos or stars shrinking from first image thru third image. I am not an expert in processing images especially blending Luminance with RGB. I seem to boost the color saturation a bit too much to bring more colors of DSOs but causes negative side effects on stars. I am still learning.

 

I have started to stop using Luminance filters due to high light pollution where I live.

 

Peter


Edited by Peter in Reno, 22 September 2014 - 09:55 AM.


#19 Peter in Reno

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Posted 22 September 2014 - 11:25 AM

This is my second DSO image (Cocoon Nebula) taken with exact same setup as my first image (NGC6946). The first image was with pseudo-Luminance added to RGB and second one just RGB. Blink in between to two images. The blue halos seem to be quite a bit less in Cocoon Nebula than NGC6946. The seeing conditions during imaging of Cocoon Nebula did not appear to be as good as NGC6946 but the stars appear to look better in Cocoon Nebula. Maybe my processing was better the second time.

 

http://peternagy.smu...escopes/Nebulae

 

I am at work right now but if you want a stack of RGB images for both NGC6946 and Cocoon Nebula, I will be happy to upload as soon as I get home from work.

 

Peter



#20 Peter in Reno

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Posted 22 September 2014 - 02:48 PM

I uploaded a stack of RGB images for Cocoon Nebula and a stack of LRGB images NGC6946. I would welcome everyone to process my images.

 

https://www.dropbox....la_RGB.zip?dl=0

 

https://www.dropbox....6_LRGB.zip?dl=0

 

My measured FWHM of each stacked images:

Cocoon Nebula: I started with Green, then Blue and finished with Red. Seeing was bad at beginning of night and progressively improved throughout the night. Blue and Green appear to show larger stars than Red.

 

Red: 3.15", 12 x 10 minutes

Green: 5.15", 12 x 10 minutes

Blue: 4.42", 12 x 10 minutes

 

NGC6946: I started with Green, then Blue and finished with Red. Seeing was not too bad all night. All images appear to have similar star sizes.

 

Red: 2.2", 10 x 10 minutes

Green: 2.82", 10 x 10 minutes

Blue: 2.82", 10 x 10 minutes

Lum: 2.88", 49 x 6 minutes

 

 

 

Star sizes in my images appear to be affected by seeing conditions. All images were auto focused with SGP and appear to be pretty accurate and consistent.

 

Peter



#21 PRejto

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Posted 22 September 2014 - 05:00 PM

Peter,

 

Thanks for posting your data!

 

It will take me a while to look through it, but I certainly will. The point I want to make (about my data) is that the FWHM values look quite decent, but still the images without UV cut in blue look very out of focus. I used a Hutech IDAS last night and had a clearly visible improvement in the look of the blue images. However, they are still rather out of focus looking. The improvement is not enough. I'm using Focusmax and it returns very sharp images in Red and Green. Also, I did not draw any conclusion about your images by looking at your color processing; my reaction is just to the look of the raw fits blue file you provided.

 

As a test of sanity, I took some blue images with the G2-8300 (astronomic filters) with no UV cut in place. There was a very very slight increase in size and a tiny amount of fuzziness. In fact it is so small I would ignore it. The Trius in comparison is unusable even with the Hutech filter in place.

 

I took a large number of exposures in blue with the Trius starting at 10 sec up to 5 minutes. I repeated the experiment 3X, and I'm graphing the data. I will post this when I finish, but I think I can say conclusively that some of the bloat is clearly due to over filling of wells. The data reveals a clear turning point. I think it is most interesting! Got to go away today so hopefully I will show this ASAP.

 

Thanks again for your help with this!

 

Peter



#22 Peter in Reno

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Posted 22 September 2014 - 08:49 PM

KAF-8300 has quite a bit less QE for blue than ICX-694 and does it help reduce star bloats for blue filter?

 

Peter

 

QE_PBernhard.jpg



#23 PRejto

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Posted 23 September 2014 - 06:05 PM

I have continued experimenting with the blue filter and Hutech IDAS. I also was loaned an Astrodon blue which made for an interesting comparison with the Baader. The Baader cuts at 380 nm, and the Astrodon at 400 nm, thus one would expect the Astrodon to be slightly sharper. This was born out in testing though the difference is subtle. The Astrodon appears to concentrate the light a bit more but still showed quite a large halo effect. With the Hutech IDAS in place in front of both filters there is an improvement as the Hutech cuts at 410 nm. To my eyes the effect was better for the Baader; I'm not sure why but I saw it after several iterations.

 

I am going to be trying out the Baader Semi-Apo filter and depending on the result may purchase a Shott GG435 as recommended by Gerd at Astronomiks. That cut might exactly match the TEC140 lens specification. What remains to be seen is how overall colour balance works with such a filter in place. A look at the graph showing frequency response of various cameras easily shows why the effect I never noticed with my KAF8300 camera is now so obvious with the Trius.

 

The other issue that clouds all of this discussion is that of star size using the Trius. It's hard to separate the two issues so I ran a bit of an experiment* with the blue filter by gradually increasing exposure times in 30 second increments up to 5 minutes. The stars in question range from about 9 to 11th magnitude. I've plotted the results. Perhaps my test had too many variables; seeing, gradually lowering altitude, tracking (I was guiding), etc. Still, the average result points to a possible enlargement taking off around the 3.5 minute mark. The reason I don't put this on the doorstep of tracking is that the aspects in CCDInspector are still quite good at the 3-5 minute positions. Anyway, I put it out here for what it's worth. Personally I do think that my 5 minute exposures have probably been too long if I want to avoid even bigger and overly saturated stars. But, even 30 seconds gives saturated stars. I wondering if in using this camera one might need to take a whole range of exposures in order to simulate the effect of deeper wells?

Peter

 

* I focused with FocusMax before each of the three runs. This was with the Baader blue filter.

Attached Thumbnails

  • Baader-30 sec.jpg
  • Baader + IDAS-30 sec.jpg
  • Size Graph.jpg

Edited by PRejto, 23 September 2014 - 06:09 PM.


#24 PRejto

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Posted 23 September 2014 - 06:06 PM

A few more attachments

Attached Thumbnails

  • AD-30 sec.jpg
  • AD + IDAS-30 sec.jpg
  • materials_schott_GG435_1.gif


#25 PRejto

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Posted 23 September 2014 - 06:08 PM

One more

Attached Thumbnails

  • CCDInsp.jpg



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