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Wha do you use to produce flats for photometry

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#1 River Hills

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Posted 27 March 2024 - 09:05 PM

I am currently working through the AAVSO intro course on photometry being taught by Ed Wiley ( highly recommended) and I did not want to get things sidetracked by asking this in the course forum. So I am wondering about what to do about producing flat frames. I have only done EAA, solar,lunar and planetary imaging and have avoided flats so far.

 

I have seen some items for sale but I am dismayed by some of the prices for some products. Sky flats are not the answer for me even though the spectral distribution is a better match than any DIY I might attempt. 

I am looking for inspiration. What have any of you done to produce photometric quality flats?

Thanks,

Rick

 

I noticed I cannot spell. Can you edit the topic title after posting?


Edited by River Hills, 27 March 2024 - 09:08 PM.


#2 SeymoreStars

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Posted 27 March 2024 - 09:16 PM

I have an observatory and use a flat panel.

 

What size aperture  is your OTA?



#3 River Hills

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Posted 27 March 2024 - 09:31 PM

Hi. I have an 8" C8. Is the panel a commercial unit or a DIY project? I have seen people on line that have used tracing panels, which seems to do the job for regular imaging but some have pointed out that some tracing pads are not uniform enough for photometry. 



#4 SeymoreStars

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Posted 27 March 2024 - 09:38 PM

It's a commercial device for a 17inch OTA.

 

The observatory is pitch black with the roof closed  and flats can be made day or night.

 

I recommend a flat panel if you have an observatory 


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#5 mrm6656

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Posted 27 March 2024 - 09:48 PM

The simple flat frame source used in the first portion of the AAVSO APASS project is cheap and easy to make and to use. It amounts to two layers of white Tshirt fabric stretched flat tightly and placed at the front of the telescope. This is then lit with light bulb(s) placed a meter or two in front of the telescope. The easy way to hold the fabric is to place it in a wooden embroidery hoop which is available at craft stores for a few dollars, US$ or Canadian$. When the hoop has a slightly greater diameter than the telescope tube, it will hold the fabric in place quite well, so long as the tube's not pointed downwards.

 

You can read about that APASS system at
https://www.aavso.or...-data-release-1
which shows a photo of the setup.

 

I usually use a similar setup, most recently substituting a piece of diffusing white plastic for the fabric. Sometimes I shoot flat frames during the daytime using the diffuser on an overcast day and pointing the telescope with diffuser towards the cloud cover. I don't see any difference from the results using the bulb and diffuser when making them this way.

 

      --- Mike


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#6 SeymoreStars

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Posted 27 March 2024 - 09:53 PM

Whatever works,  hopefully it's convenient and readily available. 



#7 GaryShaw

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Posted 28 March 2024 - 06:00 AM

Hi Rick 

 

You probably just need to do normal reading up on how to make flats…it easy enough but just a bit time consuming. I use a 30 usd led panel from Amazon so far but I’m moving to a remote observatory so I’ll be using sky flats . I tried them for the first time a month ago. After a bit of fussing with exposure, I got pretty decent flats that worked well… no tee shirt stuff… it was evening so I aimed the OTA just east of the zenith and experimented until I got it down.

Start with a led panel that has a lot of dim-ability. You want your exposures to be 2-4 secs in general, longer as needed if you include narrowband filters. Remember, you need flats ( I usually do 21 frames - more is better) for each filter and for unfiltered. You want your average adu count to be 30-50% of your full well depth. Experiment with your gear to find what corrects best for you. 
good luck

Gary


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#8 Jamey L Jenkins

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Posted 30 March 2024 - 05:42 PM

Hello,

 

For my 4-inch refractor I use a double layer of white t-shirt stretched in an embroidery hoop with a brightness adjustable flat panel from Amazon (see attached).  I also have a couple layers of high quality white paper mounted over the panel to diffuse the light even more. This panel is affordable and has performed very well for me.

 

Good luck with your photometry!!

Attached Thumbnails

  • flat panel.jpg

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#9 rutherfordt

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Posted 31 March 2024 - 05:50 AM

I use sky flats typically.

 

Tom


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#10 River Hills

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Posted 31 March 2024 - 03:57 PM

Many thanks to all for the feedback. It has  been so cloudy for so long this winter OR when clear, too darn cold for man or machine. Now that we are moving into spring, hopefully I will get a chance to try out the various suggestions. My concern about the inexpensive artists tracing pads was that they were not uniform for photometry, but I imagine that has to be evaluated on a pad by pad basis. 

Clear skies to all,

Rick



#11 KNak

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Posted 08 April 2024 - 12:38 PM

If you end up using an Ic filter almost all LED panels are IR deficient. Thats why I made my own flat box and included some 850nm IR LEDs
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#12 River Hills

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Posted 08 April 2024 - 04:03 PM

Ah, interesting point. I don't have an Ic filter but was planning on getting one. I can see this is going to take some experimentation.

Thanks,

Rick



#13 Ed Wiley

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Posted 14 April 2024 - 10:04 AM

I use a flat panel similar to the now discontinued "Spike-a-Flat" but with some near infrared LEDs included. The panel was made by Photoglow.com at my specifications. Not cheap, but Ic filter flats take 10 seconds in my current setup. What seems to be lacking in the current market is a remote switch that is ASCOM complient if you are doing remote imaging. Spike-a-Flat used to offer one; mine is custom. 

 

KNak's solution is much cheaper and no doubt just as effective (I have the same LEDs) if you are handy or (unlike me) motivated to build something.

 

Ed


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#14 KNak

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Posted 14 April 2024 - 01:21 PM

Yeah Photoglow's quote with IR added to fit my C11 came to about $350 USD, which is about $330 more than my DIY so went with my cheapo solution. And I had confirmed with Ellumiglow that their EL panels don't emit above 700nm
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