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brrttpaul

flats with mono

25 posts in this topic

Just wondering as I have always used a OSC but when you take flats with a mono do you take them with just the Lum filter only?

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You can take separate ones for each filter but I believe Mr O. Penrice of this parish does the one flat for all filters approach.

Dave

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I think it depends on how clean your filters are. If they are all dust mote free I suspect you'd get away with it. I'm sure some of the more experienced mono imagers will chime in soon...

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15 minutes ago, Davey-T said:

You can take separate ones for each filter but I believe Mr O. Penrice of this parish does the one flat for all filters approach.

Dave

He does. Well, often. There are occasions when it doesn't work so I then do a flats-per-filter approach. Doing flats-per-filter is the proper way to do it but is, I find, simply not necessary much of the time and sometimes I even find I get a better result from an L flat than from a dedicated one. Flats are funny critters. We all know the theory but we can all see a well flattened image when it's on the screen in front of us.

The most problematic dust bunnies, for me, are from contaminants far closer to the chip than the filters. Just occasionally I get a filter bunny and then a dedicated flat is the only way.

Olly

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I've experimented taking flats with no filter and all my bunnies appear to be in the camera.

Dave

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thx very much guys, it is much appreciated. Im hoping to be buying the ZWO asi 1600 next week ( still undecided on the mini or standard filter wheel), so I take it if I was to buy the bigger wheel then with the narrow band filters I do flats with them also then?  Out of curiosity is it much of a faff around if I got the miniwheel and LRGB plus HA filter then in the near future I decide I want the Si and Oi filters on a particular subject to swop them over or is it too much of a faff around. Basically I can get the mini filter wheel plus the LRGB and a HA and a phantom 3 drone lol or I can get the main wheel and the LRGB plus all the narrow bands . ( really fancy the drone I must admit)

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You can do flats for all your filters.

It's always handy to have the HA option in the wheel depending on your target, you could leave the green one out and fit O111 and synth a green.

Dave

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I've found that I need to take individual flats as I have varying degrees of banding, in particularly with my NB filters.

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I used to take dedicated flats but now I just use 2 sets both with just a L filter. 1 set for normal and 1 set 2x2 binned. 

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After Olly told me that he usually only takes luminance flats, I tried that too.

Works a treat for me :)

 

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Posted (edited)

crunch time, mini or not??? will I regret not getting the bigger wheel arrrgh EDIT gettting the mini plus HA

Edited by brrttpaul

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24 minutes ago, brrttpaul said:

crunch time, mini or not??? will I regret not getting the bigger wheel arrrgh

I'd get the bigger wheel and full set of filters, but then again a drone has never interested me. Plus you'll probably get more use out of it

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thats been the thorn in my side TBH the amount of time I get to use the dam thing with cloudy nights etc, at least with the drone I know I,ll get to use it

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37 minutes ago, brrttpaul said:

thats been the thorn in my side TBH the amount of time I get to use the dam thing with cloudy nights etc, at least with the drone I know I,ll get to use it

Maybe you can fly it high enough to see when the seemingly endless clouds end 

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um acctually ordering the bigger wheel and all the filters now:blush: wife said she buy me the drone lol

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Ordered with flo this morning so beware the impending storm of doom that will last for 6 months

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Flats are not that difficult to take and once taken generally last a while, so I take them for each filter. If you are not doing sky flats, then you can do them inside during the day. I set up a white computer screen and use a white t-shirt over the telescope end and then work out what exposure time to get 30-50% illumination. If the exposure time is too short, put another T-shirt over the end and make it longer to avoid weird banding effects of very short exposure times. Set up a run in whatever capture program you use and let it do its thing. They should last a good few months, so doing all filters is not that much of a hardship.

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4 hours ago, MattJenko said:

Flats are not that difficult to take and once taken generally last a while, so I take them for each filter. If you are not doing sky flats, then you can do them inside during the day. I set up a white computer screen and use a white t-shirt over the telescope end and then work out what exposure time to get 30-50% illumination. If the exposure time is too short, put another T-shirt over the end and make it longer to avoid weird banding effects of very short exposure times. Set up a run in whatever capture program you use and let it do its thing. They should last a good few months, so doing all filters is not that much of a hardship.

Surely that's only a plan if your setup is permanent, I don't see how to avoid taking flats every session if you setup each night.

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Olly advised me some years ago that if your filterwheel is an enclosed one (i.e. not a manual one where dust could get it)  then you only need to do luminance (or Ha) flats, but I have never been brave enough to chance that until recently.  I do take separate flats for anything binned, but interestingly (and I have had this conversation with Olly), I forgot to do binned flats last image, so for the hell of it I chucked in the non binned flats to see what would happen in Astroart, and to my surprise (and Olly's) it did not reject them.

I guess if you have a closed filterwheel , you could take a set for each filter first time around, and then try stacking with just the luminance flats for the RGB and see whether it will work.  Have been meaning to do that myself for some time, but keep forgetting.

Carole 

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11 minutes ago, John78 said:

Surely that's only a plan if your setup is permanent, I don't see how to avoid taking flats every session if you setup each night.

I set up and tear down every night. If you leave the camera attached to the scope and don't shake it about, flats work fine, until they don't, when I retake them. This is usually measured in multiple months.

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To be honest, I ordered the camera, the large wheel plus lrgb plus the three narrow bands  and I have also ordered a new computer so everything will be from scratch, I have also worked out that my obsy will cost me less than a £100 to build as the pier is there and the base so its just a matter of a pack of blocks some wheels and steel and marine ply roof. Now the panic is starting to kick in as I realise what i have just done lol (seriously I do panic for no reason).  As I will be starting from scratch im thinking SGPRO for my sequence and CDC plus PHD2, PI to process, they seem to be the most popular (I,m using maxim ATM along with astrototilla and been guiding through maxim but Im really not sure how ZWO camera gets along with maxim and as im starting from scratch I dont want to say try maxim out find it dont work then go to use SGPRO and then that wont work because I have fluffed something drivers etc. Its a headache and it hasnt even arrived yet lol

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Fine line between panic and excitement! SGPro works well with the ASI1600 - I use it myself. I also use CDC as opposed to Stellarium to do the initial pointing and the PlateSolve2 software that SGPRo uses I found much better than Astrotortilla. PHD2 is good, although can take a while to know well, and I am still learning. There is a great astroimagingchannel video on youtube about using it from one of the developers.

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Oh believe me I have watched endless youtube vids and have been going over it and over it constantly. I have just been watching one for sgpro think his name was broke astronomer? something like that and it was very good he also touched on phd2 (in fact i think I will watch it again now) he was also showing the plate solving with sgpro  and I really liked that , the plan will be just to use sgpro eventually, as a side note your name rung a bell and pretty sure I have been following your pictures on astrobin

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Yeah, I use astrobin to record all the subs etc against the images, as I don't make any other kind of log! My best images have come from my ASI1600!

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