Flats idea

[Terrierist]

I used to live stream quite a bit in an old job and had this Iographer iPad holder as part of my kit.

I'd read that flats can be tricky to shoot and wonder if you think that the following set up would give good results - as I'd never managed to shoot flats previously. 

Basically, I've created a white image in Photoshop and then used it as an image on my iPad to take flats with, slotted the iPad into the iOgrapher and placed it as shown.

What are the pitfalls, how could I make this better? I have used Astrophotography Tools CCD Flats Aid to take some images.

Thanks for any advice.

[Guest Tuomo]

Many astrophotographer uses laptop/ipad screen to make flats. To me theres nothing wrong with this. I use Huion A4-sized drawboard. Maybe use white old t-shirt and cover up the scope to make sure sensor is evenly illuminated.

[ollypenrice]

I, too, would use this in the dark or put a black shroud over it. You are also likely to need a way of dimming it to the right level as stated above.

Olly

[Terrierist]

6 minutes ago, Tuomo said:

Many astrophotographer uses laptop/ipad screen to make flats. To me theres nothing wrong with this. I use Huion A4-sized drawboard. Maybe use white old t-shirt and cover up the scope to make sure sensor is evenly illuminated.

Thanks for the reply and advice, I did wonder if I needed something to diffuse the light

[Guest Tuomo]

Just now, Terrierist said:

Thanks for the reply and advice, I did wonder if I needed something to diffuse the light

Sometimes I still use old white T-shirt and point scope to blue sky. It gives surprisingly  good results. Make sure you are not pointing near sun as it could give you bad flat.

[Guest Tuomo]

BTW, I think your Polemaster USB port should point to the left side of the scope.....

"Retreat the thumb screw and insert the electronic polar scope.
Align the USB port to the left side, as shown in the photo.
This will ensure that the image will be moved by altitude
and azimuth adjustment accordingly. Tighten the thumb screw to lock the polar scope in
place."

 

 

[Terrierist]

6 minutes ago, Tuomo said:

BTW, I think your Polemaster USB port should point to the left side of the scope.....

"Retreat the thumb screw and insert the electronic polar scope.
Align the USB port to the left side, as shown in the photo.
This will ensure that the image will be moved by altitude
and azimuth adjustment accordingly. Tighten the thumb screw to lock the polar scope in
place."

 

 

Wow! Hadn’t realised you needed to do that. Will revisit the instructions. Thanks, Tuomo!

[Zakalwe]

I use a LED ceiling tile, dimmed down with about 5 sheets of white A4. I just point the scope straight up and pop the tile on top of the dew shield. This ensures even illumination with no stray light intruding to vary the average ADU.

it's important to make it dim enough to ensure that the exposure is not too short. LED and CCFL light sources can flicker very fast and this can cause rolling shutter artefacts in the flats. This would lead to incorrect calibration.

As long as the flats are over a second or two then you should be right.

[Terrierist]

1 minute ago, Zakalwe said:

I use a LED ceiling tile, dimmed down with about 5 sheets of white A4. it's important to make it dim enough to ensure that the exposure is not too short. LED and CCFL light sources can flicker very fast and this can cause rolling shutter artefacts in the flats. This would lead to incorrect calibration.

As long as the flats are over a second or two then you should be right.

Thanks, you have helped me there as I didn't understand the length required, I'd read that an ADU 0f around 20000 was all that is required - my flats are around 1/2 a second.

[Zakalwe]

20,000 to 25,000 seems to be the norm. I don't think that it matters too much as long as the flats are consistent.

Personally I'd dim the light and stretch the sub length a bit. 

Sequence Generator Pro makes taking flats a cinch. It has a Flats Wizard...you tell it the target ADU and it automatically runs a series of exposures to work out which sub length gives the right value.  It then saves this value for future use. 

[souls33k3r]

Apologies in advance OP. Just a side question, i see you're mounting you 9x50 finderscope and using it as a guidescope with a QHY5L guidecame i presume. How are you connecting it? I also see the silver O ring that comes with the guidecam. Any close-up picture of this setup?

[Terrierist]

20 minutes ago, souls33k3r said:

Apologies in advance OP. Just a side question, i see you're mounting you 9x50 finderscope and using it as a guidescope with a QHY5L guidecame i presume. How are you connecting it? I also see the silver O ring that comes with the guidecam. Any close-up picture of this setup?

Hello! Yes, this is correct, to be honest I don't use it as I am struggling getting PHD2 to work well with it. That is probably down to my lack of knowledge with guiding. I live in a very light polluted area so tend to image  at 90 seconds maximum, so don't need to use the guide system. When it is connected, I connect from the guide camera to power box on the EQ5, where it says 'Autoguider'.

I'll PM you some images later.

Kev

[souls33k3r]

1 hour ago, Terrierist said:

Hello! Yes, this is correct, to be honest I don't use it as I am struggling getting PHD2 to work well with it. That is probably down to my lack of knowledge with guiding. I live in a very light polluted area so tend to image  at 90 seconds maximum, so don't need to use the guide system. When it is connected, I connect from the guide camera to power box on the EQ5, where it says 'Autoguider'.

I'll PM you some images later.

Kev

Ah ok, no worries mate, PM me when you can. Was just interested how your camera was connected to the guidescope because i'll be doing the same. The O ring got me interested as well so just trying to steal an idea  Cheers matey.

As for the guiding, i live in the light polluted area as well but guide up to 5 min without any issues (only because i don't like taking longer subs with a CMOS camera). I'll reply to your PM and can give you a few hints and things as well