Flower Pot Flats - The Test

[Marky1973]

Sorry for starting a new thread, but I thought I would post this separately with a bit of info on how I made my flowerpot and some examples of some test shots I made last night that show the difference it made including flats. I doubt it is very scientific, but it seemed to make a difference to me.

So, first things first, what did I make?

INGREDIENTS

1. Flowerpot - larger than the aperture of your scope
2. Light source - in my case an LED light that was lying around - couple of quid from B&Q
3. Silver Foil
4. Tape
5. A white t-shirt

 

 

[sorry the photos are at a funny angle, but I couldn't get them to show the right way around - probably because I took them on my phone - if  a mod is able to change, that would be fantastic]

I used a black flowerpot, but the colour probably doesn't matter as I covered the inside with Silver Foil, all held down with tape to keep it secure. My first effort didn't spread the light very well, so I added the foil, with the duller side outermost and that helped spread the light more evenly around the pot

I then cut a small circle from the T-Shirt to cover the LED Light, held on with a hair band as that was lying on the table when I was cutting the T-Shirt. This was just because the LED on it's own was too bright and the light was not even across the whole "lamp" when it was finished. I used just one layer of the T-Shirt, but you can double it up if it is still too bright.

The LED light has a magnet on the underside, which was quite handy, so I taped a metal washer to the outside of the bottom of the flowerpot, so that I could attach the LED to the inside of the pot like a light bulb in a lamp shade. If you can, get a magnetised one as it is a lot easier, although I suspect you'll be able to find other ways to attach the LED.

Switched on

Then I took the T-Shirt, cut it up into a convenient size and covered the Pot aperture with a double layer of material.

Switched on

Obviously if you so this and it is too bright, you can add more material to the LED lamp or the Pot aperture but, for me, this method achieved a very even spread across the pot.

But, the proof of the pudding and all....

So I went out last night to try some more shots of Andromeda. A previous effort showed vignetting and I was recommended to use Flats by another member to reduce that effect.

So:

Starwave 70ED, unmodded Canon 1100d, EQ3-2 with RA Motor.

20 x 90 second lights

20 Flats (AV setting on camera) simply holding the assembled pot over the Scope aperture (Histogram was centrally positioned)

20 x 90 second darks

20 x Bias at 1/4000th

I wanted to take more frames, but didn't have the time last night....next time....

I then stacked the pictures in DSS (18 out of 20 frames were stacked)

Once WITHOUT the FLATS

And once WITH the FLATS

I kept everything the same in the settings to make sure the process was the same for both and the same minimal processing in DSS. But, as I said, I am sure it is not very scientific, so there is probably some room for error.

I then went to GIMP to process and did the same, very basic changes as per a rough and ready guide from Steve Richards that I googled. Which was esentially a use of the LEVELS dropper to darken the background, Gamma adjustment, the same level of sharpening, a little RGB tweak and some saturation.

Again, it is not very scientific, but the image WITH the FLATS

is obviously much better than the one WITHOUT.

They still aren't great pictures but, considering the low number of subs and the big bright moon that was chasing Andromeda last night, I was quite pleased with the results.

Will definitely use the Flower Pot again and see what other results I can get with it on some other targets.

[Marky1973]

Apologies for the formatting on the list of ingredients.....I have no idea what happened there.....didn't see it in the preview. (I'll be glad when I can edit posts!) ;-)

***now updated***

[happy-kat]

Very noticeable difference with the flower pot used.

Will you be able to use one set of images for all images or will it be use the flowerpot every time?

I had been wondering how I was going to (of I ever did) create flats as our laptop is bust but this is a doable alternative for me.

[Marky1973]

Happy-Kat, I was kind of presuming I would need to take them each time to ensure they were taken under the same conditions, but I can always have a play and see what happens if I use them again. My imaging is usually going to happen at similar times, so perhaps they can be used for Andromeda again.

Having said that, it wasn't a particularly inconvenient thing to do. I only took 20, which took maybe a minute or two. The hardest thing was holding the flowerpot up to the scope while takingthe photos - next time, I'll take my remote with me! Or set up an imaging run.

Definitely worth a go though. I am sure everyone's results would vary depending on the light source and the material but, as I had everything in the house already, I've not spent or lost anything having a go.

(Well, other than the T-Shirt, but that was a "novelty" that I was given for my 40th Birthday with a fake newspaper print  of all the stuff that happened the year I was born - and I was never going to actually wear it.....)

[pyrasanth]

i like these pictures. I had the same issue the other night when I tried the Hyperstar without filters. The detail got completely washed out. I'm going to try again with a CLS filter to cut out the sodium light. I'm also going to look at critical focusing using focusmax as I think my last image had focus issues. I will try lots of 30 second exposures to try & keep the core from not over saturating. The moon was a real killer & I think it contributed to, with the street light below (sodium) a very disappointing first attempt.

[Marky1973]

Thanks Pyrasanth - there really is so much to think about, and I am already thinking about the next step and how to make the pictures better. Keep looking at LP filters and reading about ways to balance the exposure across the image to reduce the saturation at the core. Complicated stuff! Hoping the current rubbish weather lets up a bit next week so I can have a play tunder a new moon!