Flats question ....:O)

[Moon monkey]

Hi everyone I think its about time I learned how to add flats to my images Is it ok for me to remove my scope from the tripod after an evenings imaging, with the camera and focus un altered. Then take it inside and do my flats with the laptop screen and a taught white t shirt over the front ? (of the OTA... not the scope ) Hope you get what I mean

ps .. do i keep the same iso ? and can I take the pics with the camera in auto ?

Cheers MM

[Martin-Devon]

Yes - as long as the entire imaging train is unaltered then you can indeed remove the scope from the mount as you suggest and take the flats indoors. Others will need to comment about the iso values though since I use a CCD not a DSLR.

[swag72]

You will need to keep the ISO the same as your images. If I remember correctly, you set the camera to AV and adjust the shutter speed accordingly to get the histogram 1/3rd - 1/2th across.

[Rustysplit]

I leave the iso setting the same. With a canon you can i believe use the auto setting.

[Moon monkey]

Thats fantastic .... thanks for thr replies

Cheers MM

[allcart]

You can't set av and alter the shutter speed without changing the aperture. I'm sure you should keep the aperture the same as you used for the imaging session. You might add a bit of exposure compensation to move the histogram to the right, but I'm not sure that is acceptable. TBH, I have had no luck using any kind of screen. When I tried it, I got dark bands running down the images caused by the screen refresh rates. I think you would need a pretty slow shutter speed to avoid it, but at f.4 and wider the shutter speed is just too quick.

I settled on the bright sky with a diffuser method.

Side note: you could set the cam to manual and choose any shutter speed and aperture you like to place the histogram anywhere you want.

[Photosbykev]

You must not adjust the aperture as this has a clear effect on vignetting and the visibility of dust bunnies.

You adjust the iso, shutter speed and light panel intensity (if it's adjustable) to get a peak on the histogram in the centre. If you do switch to Av or manual ensure you reset the aperture to the original setting if you use a DSLR lens, if you use a scope then the aperture can't be altered anyway

[Moon monkey]

I dont think I can adjust the aperture can I ? the camera is attached to the scope and the scope is F4 ... not sure how I can take flats before I image on the chosen night ? I wont know the focus or orientation of the camera ?

Cheers MM

[allcart]

good points Kev, I always assume folks are using lenses with dslr's. Therefore you cannot change the aperture but do as others have said and adjust shutter and Iso.

No I don't see how you you could do flats in advance either.

[Tim]

Be very very wary of bringing a cold scope/camera inside in this weather, the typical moisture in the air in a warm house will condense rapidly on cold glass and surfaces and could completely mess things up for you.

[Ant]

If you get stuck MM, give me a shout and we'll see if we can get together over the Christmas break... I live in Coates which is about 9 miles from Peterborough.

i'm no expert but I can certainly show you what I do.

Cheers

Ant

[kirkster501]

Flats don't take long though..... I can fire all mine off in less than 5 minutes........ Is it worth bothering bringing the whole imaging setup inside for the sake of five minutes more time before packing away?

[ollypenrice]

I like flats to be durable so I try to leave the imaging train unchanged between images, at least during one new moon spell.

Ollyu

[Moon monkey]

If I

I like flats to be durable so I try to leave the imaging train unchanged between images, at least during one new moon spell.

Ollyu

Thats exactly what I will do once I have an observatory

[Moon monkey]

Flats don't take long though..... I can fire all mine off in less than 5 minutes........ Is it worth bothering bringing the whole imaging setup inside for the sake of five minutes more time before packing away?

Thats very true what light sorce do you use please ?

[ollypenrice]

Thats very true what light sorce do you use please ?

It's hard to beat an EL panel. We use Gerd Neumann panels here but FLO were looking into a UK supplier of something similar.

Olly

[kirkster501]

Thats very true what light sorce do you use please ?

t shirt and elastic band round front of scope then a piece of A4 printer paper then iPad with white screen. Set 20 flats program in APT and fire away.

[swag72]

Homemade light panel for me - An A5 EL panel from Earlsmann and a couple of sheets of 3mm opal perspex - All held together in a rather fetching wood frame made by my hubby!

Works a treat!

[opticalpath]

Homemade light panel for me - An A5 EL panel from Earlsmann and a couple of sheets of 3mm opal perspex - All held together in a rather fetching wood frame made by my hubby!

Works a treat!

Very neat too. You could mount a photo on the other side and hang it on the wall when not in use!

Adrian

[kirkster501]

I am going to make one of those panels as well. My idea is to get an A4 Earlsman Panel and an A4 picture frame from IKEA with perspex already in front. Bob's your fathers brother......

Juts a question of how to power it up. Any options from a car fag lighter?

[WaveSoarer]

I'm thinking of doing some flats too. How often should these be done? The reason I ask is that the CCD detectors I work with for X-ray crystallography, which are peltier cooled to -45 C with all the cold parts held under high vacuum (they are extremely expensive pieces of kit by the way) have their flat images (flood fields) measured once in the factory. These last the life-time of the detector unless a repair is required. The dark frames are recollected on a regular basis, though, and we have a stack of these for different exposure times. I'm just wondering if it's really necessary to acquire flat images for every imaging session. Unless there is a significant change to the CCD sensor I would find it surprising that flats would need to be taken all that frequently. I expect dust on the CCD sensor would be the most likely issue unless the optics of the telescope has an effect that can vary between sessions (such as the orientation of the camera on the focuser). What experience do people have with using sets of old flat images?

[Moon monkey]

Brilliant help everyone Im starting to formulate a plan now I fancy making a light panel ... If I use the lap top screen I get lines across the image, think its because I have an F4 scope and cant get a slow enough shutter speed .... I take it the light panels dont flicker ?

Cheers MM

[ollypenrice]

I'm thinking of doing some flats too. How often should these be done? The reason I ask is that the CCD detectors I work with for X-ray crystallography, which are peltier cooled to -45 C with all the cold parts held under high vacuum (they are extremely expensive pieces of kit by the way) have their flat images (flood fields) measured once in the factory. These last the life-time of the detector unless a repair is required. The dark frames are recollected on a regular basis, though, and we have a stack of these for different exposure times. I'm just wondering if it's really necessary to acquire flat images for every imaging session. Unless there is a significant change to the CCD sensor I would find it surprising that flats would need to be taken all that frequently. I expect dust on the CCD sensor would be the most likely issue unless the optics of the telescope has an effect that can vary between sessions (such as the orientation of the camera on the focuser). What experience do people have with using sets of old flat images?

SInce I have square chips I rarely change the camera orientation. I do a set of flats for a new moon period and hope to use them on all images for that dark time. Of course I sometimes change scopes or add/remove the reducer and that's that. New flats.

It's not the detector that changes so much as new bits of grot in the train, little spots of organic growth on the chip window, that kind of thing.

In a nutshell if you are observatory based it's usually only changing orientation that will make your flats obsolete. SInce few things in life are as dull as doing flats 'I think this is good!!'

Olly

[RikM]

Brilliant help everyone Im starting to formulate a plan now I fancy making a light panel ... If I use the lap top screen I get lines across the image, think its because I have an F4 scope and cant get a slow enough shutter speed .... I take it the light panels dont flicker ?

Cheers MM

You could add a few sheets of white paper to dim / diffuse the screen and reduce the shutter speed. That would help with reducing banding.

[Moon monkey]

Sounds like a plan Rik ... thanks just need some clear skys now no doubt the moon will then be up !!!!