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Decent quality flats for DSLR

julian489289

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julian489289

julian489289

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I am looking to get some good quality flats for my astro images that I take with my Canon 650D DSLR & 102 mm ES Refractor.

I am looking to buy an EL panel -  http://www.amazon.co.uk/dp/B00J3NRAV2/ref=wl_it_dp_o_pC_nS_ttl?_encoding=UTF8&colid=1V71YJQYGR6X3&coliid=IUV4AUJBRS1C3&psc=1

The LB4 priced at £59.99 seems good value compared to Gerd Neumann's panels.  Would this do a satisfactory job as I note that you can even adjust the brightness of the panel to get the right saturation??  Any thoughts comments?

Also what procedure should I be following.  I usually just set my DSLR to AV mode at the same ISO as my lights, place a laptop screen over the lens using visual light box (VLB) and snap away with my intervalometer.  I have no idea as to whether the result flat is of good quality  I can never see any dust bunnies of vignetting on these flats that I take.

I read that you should work out the correct ADU for your specific camera (usually 20000-30000) and that Maxim DL can reveal this value with your subs.  Unfortunately, I do not have this software. I use DSS, APT & CS6.   How do I work out what my ADU is?  Also I read that the flats should be 65-70% of the histogram but not over exposed.  Is that 1/3 in from the right?

What is the best way/procedure to take my flats?

Hope you guys can advise me, thanks

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Bizibilder

Bizibilder

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I use one of those panels for flats and they work very well.  Just put the panel on the end of the scope (I put the scope vertical to do this), the camera on Av and have the panel on or about its dimmest setting.  This will give an exposure time of about 1/5 - 1/3 sec which seems to work well.  if you have the panel too bright then you will see shutter shadows on your flats - these are really obvious black bars across the flat.  I've never considered ADU values and never look at the histogram and my flats work OK!!

If you have a 102mm refractor then you only need the A4 sized panel at £35.99.  there is no discernable "middle" on these panels - you can use them right up to the edge.

The only other suggestion I would make is to buy a foam rubber laptop case to keep the panel in - they are quite fragile, especially the plug and socket connection to the cable, it is small and easily damaged.

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julian489289

julian489289

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Thanks Guys.  It seems strange that something at this price point does the same as Gerd's Flatfield panels with the right colour spectrum and uniform brightness.  I have corresponded with Gerd who has been very helpful however, believes that his panels maybe too bright and has suggested the addition of his ND foils to reduce the energy output to suit my DSLR.  However this takes the price to 150 plus Euros plus postage!

Roger that procedure sounds similar to what I have been doing with the laptop screen.  However, why do I not see the vignetting or dust bunnies on the flats that the camera takes?  They usually just look blue ish subs??  I take it 1/5 to 1/3 exposes at 1/4 in from the right of the histogram (75%)?

Thanks Peter that looks the same as the Amazon one but seems to come from China??

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Psychobilly

Psychobilly

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They stated UK stock and It's been despatched and should be with me on Tuesday or Wednesday...

A mate works for a sign making company and is going to get  me some off cuts of the opalescent film they use for backlit printed signs...

In the past I have used drafting film or laminating pockets to reduce the brightness of the EL panel...

I have picked up some Kodak 2000mAH Li-ion USB Smartphone "emergency" chargers that were on offer from the local Esso garage to run the pad - they have 1A output capacity and are recharged using the smartphone charger...

Peter...

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frostynixon

frostynixon

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Thanks for sharing this lightpanel. I`m also looking for a flatfield panel as my Newton vignettes quite severely which means that i didn`t rotate the camera during the night.

With this device i can take flats on the fly at a reasonable price!

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sharkmelley

sharkmelley

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My best quality DSLR flats come from using a light diffuser panel over the end of the scope in daylight - a "white cloud" day rather then a sunny one.

Search for "3mm OPAL ACRYLIC 500 x 500 mm Light Diffuser Sign Box Plastic Sheet Panel" on eBay - less than a tenner.

http://www.ebay.co.uk/itm/400143709684

Taking manual exposures, increase exposure length until part of the image just begins to saturate and then back it off by 1 or 2 stops.

Mark

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julian489289

julian489289

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Thanks guys, Olly you have  helped me to make my mind up. 

Peter, it does say that the light box does dim but do you think not quite enough as to why you are adding these sheets?  Could you please update this thread when you get yours with your thoughts?

Mark, sorry if a daft question but how do you tell when the images just starts to saturate?

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sharkmelley

sharkmelley

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Mark, sorry if a daft question but how do you tell when the images just starts to saturate?

It's not a daft question.  View the image on the rear LCD and repeatedly hit INFO to cycle through various displays of the image - histograms etc.  One of those displays flashes any saturated areas of the image.  It might also be obvious from the histogram bunching up at the right hand side.

Mark

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Psychobilly

Psychobilly

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Panel Arrived today had both Chinese and English postage labels on it... But UK delivery was Parcelforce 48  and they don't include weekends in the 48 hours so I guess it was shipped from the UK in the same packaging that the seller had it from China... The seller is now "closed" for a few weeks due to  the Chinese new year

Just tired it running it from one of the Li-ION packs runs fine the waving finger spread hand test shows the panel is being "scanned"  I should dig out the detector and digitizing scope and find out what frequency it's beign scanned at...

With the 7DII at ISO 400 and 200/2.8L with the IDAS P2 filter fitted at f3.5 the exposure range on Av went from 1/250s at the brightest setting to 1/15s at the lowest the lower setting showed banding the higher one was fine...

I will do a flat with a random flat test  this should show up any variation coming from the scanning...

BIAB...

Lowest brightness setting 1/15s exposure single flat frame staked with master stack of 10 frames extreme stretch in PS CC 

Lowest%20setting%20single%20flat%20with%

Lowest brightness setting 1/15s exposure single flat frame staked with master stack of 10 frames Analysis in PS CC  RGB Histograms and Image Stats  (Un-stretched image)

Lowest%20setting%20single%20flat%20with%

Highest  brightness setting 1/1250s exposure single flat frame staked with master stack of 10 frames extreme stretch in PS CC 

Highest%20setting%20single%20flat%20with

Highest brightness setting 1/1250s exposure single flat frame staked with master stack of 10 frames Analysis in PS CC  RGB Histograms and Image Stats  (Un-stretched image)

Highest%20setting%20single%20flat%20with

Single Flats - color cast comes from IDAS P2

Lowest Setting 1/15S exposure time

Low%20%20Setting%201-15s%20Banding.jpg

Med Setting 1/200s Exposure time...

Med%20Setting%201-200s%20Banding.jpg

Highest Setting 1/1250s Exposure Time

Hi%20Setting%201-1250s%20Banding.jpg

Peter...

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julian489289

julian489289

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Thanks Peter for that detailed reply.  I think I will get one!

Strange how SuperGiant has his on the dimmest setting to get 1/5 - 1/3sec and gets good flats but too bright he gets shutter shadows and yours is on the highest brightness to achieve the same.  Why would that be?

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Xplode

Xplode

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I have used an L4S version for a while and find it great.

I always set it to dimmest and chose ISO100 on the 6D, exposure time is around 1s on my scopes and lens at f/5-5.8.

A new 12" f/4 newtonian has been ordered so i have bought a A2 version which is hugh, but i haven't tested it yet.

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ollypenrice

ollypenrice

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Typically these LED panels are dimmed electronically  by adjusting the duty cycle of the LED drive waveform... I still haven't found my photo-diode probe for the scope  to actually capture the optical output waveforms...

Peter....

Sometimes I'm frightened of Peter...

:eek: lly

:grin:  :grin:  :grin:

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julian489289

julian489289

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Thanks Guys for all of your helpful comments.

I have taken various flats using my visual light box screen on my laptop.  VLB at its brightest is set at 255 and lowest setting the dimmest is 0.

Setting my camera (650D DSLR) to AV and taking my flats I get the following;

VLB Setting      Exposure     

255                   1/100

200                    1/80

150                     1/50

125                    1/40

100                    1/25

50                      1/8

30                       1/4

20                       0.5"

How can I tell what is the best setting on the VLB (brightness) to suit my best flats.  The higher the brightness they are darker grey and as I drop down in brightness the grey lightens up and then to shades of blues at the lower settings.  All look even and no banding can be seen.  

Should I be looking at the 100 and below setting?  What am I looking for in the flat as they all look the same to my untrained eye??

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Psychobilly

Psychobilly

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Looking at the exposure times for the various settings they are all  OK  ... You want to look at the histogram of the exposure rather than the exposure time...

Have a look at RikM's post here...

http://stargazerslounge.com/topic/171079-light-dark-flat-bias-frames-with-dslr/?p=1744378

Depending on the ISO you have shot your lights at ,  a very bright panel might end up with exposures that are  shorter than the min exposure time of the camera...  your no where near that...

Peter...

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julian489289

julian489289

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Pete, that has confused me even more, the more that I question, the more confused i get. :huh:

For 1/125 to 1/8 all seem to be mid histogram.  1/250th was 1/3 histogram.  However, my peaks are pretty narrow not as rounded as the ones pictured in that link, is that right?  Are all of these flats usable?

I note from the link for different ISOs you should do different exposures. ie 1/250 for 1600ISO & 1/180 for 800ISO, is that right??

There seems to be that many different flats that you can end up with, how do you know that you have the right flat at the correct exposure, that question is really confusing me?  

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