Taking widefield images on a static tripod

[happy-kat]

I've never tried it but seen great images from doing it. Sometimes you just got to have a go and you have a garden and a tree.

[ianpwilliams]

I'm coming back to this now that October is approaching. I've now bought a 55-250mm IS lens for the trip so I won't have to rely on a tripod for daytime wildlife shots. And then I've got my stock 55mm lens as well. So my hope is that I can use the 250mm lens in the daytime and the stock 55mm lens for Astro.

 

I've got two filters - one is a UV filter (which my dad advised me to buy partly for the UV filtering but also because it protects the lens), and also an LP filter which I bought for using in the back garden when imaging with the scope. I'm guessing that I wouldn't need to use both a UV filter and an LP at the same time on the same lens, is that correct? In which case I could have the UV on the 250mm and the LP on the 55mm. Although our base on this trip is apparently quite remote so maybe I wouldn't need the LP at all. If there's little to no light pollution, will using an LP filter cause issues? Or can I just leave it in regardless?

 

Also, I recently had the opportunity to take some Astro photos in a fairly remote place. When looking up with the naked eye I could have sworn that I saw a very faint Milky Way band across the sky, but it didn't show up in the photo. It was a static tripod so I had a limit of about 6 seconds to work with, and although I took various shots I was experimenting with different sub lengths to see when star trails appeared, so there may not be an opportunity to stack. So will it be worth processing single shots in PixInsight do you think?

[happy-kat]

I haven't thought about it but I leave my UV filters on my lenses all the time and then add the LP filter using a step ring as I only have one of those in 2inch flavour and uses step up or down rings to fit it to my lenses. I've got a 58mm down to 48mm step ring that then gets the lp filter on it which I can use on the kit lens and the 85mm (I have other size step ring for my vintage lens). This ring gives a slight aperature step down which is OK. If there is no LP I wouldn't bother adding it to my lens. Whether I should stack the filters or swap tham I don't know I just do what works for me and keeping the lens clean and not dropping stuff in the dark.

Your 6 second shot may not have been long enough I would have thought the kit lens on 18mm would have given you more like 20 seconds.

[ianpwilliams]

Thanks, I'll probably go with UV on the long lens and LP on the short.

 

As for 6 seconds, that's because I only had my long lens with me which is 55mm min. Will use the short lens on the trip.

[ianpwilliams]

I had a go at some widefield imaging in the back garden last night. There were a few clouds unfortunately, but I still had a chance to achieve focus and try some different sub lengths. I took the following:

 

10 Lights - f4, 17 seconds, 400ISO, 18mm

12 Flats

5 Darks

20 Bias

 

I stacked everything together and stretched the TIFF (top left in the screengrab), and I also stretched a single Light (bottom right in the screengrab) to compare and contrast. For some reason the stretched single Light seems to be better.

 

I'm aware that when I rested the iPhone against the lens to take Darks and Flats (I left the lens cap in my flat so I had to use my iPhone, and I used my iPhone with a blank white image for the flats) the lens moved a little bit, which I guess may have altered the focus a little bit too. So maybe that could be why the stacked shot doesn't look so good.

 

I also attempted to lock the focus ring in place by putting some tape across the lens from the static part to the moving part. Unfortunately there is now a very thin, plastic ring around the lens which moves around freely, and which shouldn't be. Does anyone know why that might have happened, and whether it will cause a problem? Either way I'll put the lens cap on for Darks in future, and I'll point the camera downwards to take the Flats so that I can rest the iPhone against the lens without applying pressure to it.

 

 

[ianpwilliams]

This is just the Lights stacked together and then the TIFF stretched in Pix (nothing else done yet). I quite like it actually.

[happy-kat]

Looks like good focus.

See if the ap lightbox can be used on your phone much better as it has a slider bar to easy adjust brightness so you can get the histogram where you want it more easily for flats.

I don't find my kit lens focus slips, I have the camera using back button focus and the lens on manual once focused back to auto. With using bbf can use shutter button and focus doesn't change. But I've not had a chance to play again yet this season to see if that works for me with my new Canon lens.

Do you think focus would have slipped with out the tape?

[ianpwilliams]

Yes I keep forgetting about BBF, I'll research that tonight.

 

I'll have a look at that app, although in AV mode at 100ISO the histogram was always bang in the middle for my flats, so hopefully they might be ok.

 

As for focus, I gave up on trying to hold the focus ring in place in the end, but you can see from the results that it held focus ok anyway. So maybe it'll be ok, although if BBF can make absolutely sure then maybe I should consider that. Or I could try Blu Tak, but I'm less keen on that.

 

I'm still a bit concerned about the ring that's come loose though. It almost looks like a thin rubber band, which is now loose. Will it be a problem I wonder?

[ianpwilliams]

I'm looking at back button focus. So the back button has to be pressed for the camera to focus, rather that the shutter button being pressed halfway down. But surely that's only applicable if you're using autofocus isn't it?

 

Let's say I'm in manual focus mode. I increase the ISO, bring up Live View, and manually focus on a bright star. Then I put the camera on the ground on its tripod (I'm using a mini tripod). If I were able to then press the back focus button to lock the focus then that would be great, but it sounds like it wouldn't do that. Although if I were to get my focus and then switch to autofocus, would that mean that the focus would technically be locked because I would need to press the back focus button for the camera to autofocus?

 

The other consideration is that I prefer to use my timer remote than the shutter button because it's easier to take lots of shots. I don't know if that would affect anything?

 

When it comes to calibration shots I'm not so sure if it'll be worth bothering with those, so I'll be tempted to just take as many Lights as possible to make the most of the time available.

[happy-kat]

Once the camera is focused it is focused. All bbf does is take away focus from the shutter button, so no risk of pushing shutter and changing focus. I focus manually even with bbf enabled, once I'm happy with focus I slide the lens switch to af, I hope to try this with my new lens though I'm never outside very long and haven't noticed lens slip when I forget.. Great you have a timer remote that makes it easier and probably don't need to look at bbf then, but it is a neat thing to know about. 

I don't have a rubber band l like ring on my kit lens that I can see.

Your flats sound fine.

[ianpwilliams]

Thanks, looks like I'm all ready then. Just hope I get clear skies...

[happy-kat]

It's probably worth doing another practice and check your focus/lens is holding post tape/loose bit 

A trip to the warm sounds very nice.

I would probably take some bias frames too as easy and very quick to go with the flats and maybe a few darks I'd hate to not have quite enough.

I need to check my flats as I think I'd been taking them with the same ISO as the lights. I hadn't clocked you'd put iso100.

 

[ianpwilliams]

Yes I'll try another practice, although I'm sure it'll be fine. And even using the timer remote I'm guessing I should switch to autofocus once I have focus because I guess that might mean that focus is more likely to hold.

 

When using the telescope I started taking my flats in manual mode because in AV mode at 100ISO the camera was taking really long exposures. But when just using the camera and doing AV mode and 100ISO the exposures are nice and short and the histogram is always bang in the middle.

 

Although I'm still reluctant to bother with calibration frames. I'll either go all out and do flats/darks/bias, or do no calibration frames at all and just do as many lights as possible instead. It'll depend on how much time I have (probably not much).

[happy-kat]

Maybe do some let's assume same focus distance and iso, take one load and share them when later processing as it is unlikely once you decide what ISO and aperture to use that it would change I guess the variable is you are using a zoom lens... Hadn't thought of that as I use a fixed lens.

Not sure if focus holding can be relied on if using AF and not BBF.

[happy-kat]

When you see single image photos in the 'astro holiday plans' thread perhaps it can be kept simple.

Have a great time :-)

[happy-kat]

You might like to read again about flats, I have had another look and I think they are to be the same ISO/aperature/focus as the images they were taken to go with. Looking at mine their shutter speed is the variable to get the histogram in the middle.

I do like to take bias frames they are so quick, I keep reading about darks and whether they add more noise or not, when I can eventually get some images to play with I think I might try some testing without darks but with flats and bias.

[ianpwilliams]

I started another thread asking if extra lights or calibration frames are the way to go and most people think that for just the camera it'll be best to go all out for lights. It also looks like darks won't be worth it, bias are easy (although maybe pointless unless I do flats too), and flats are the tricky one. I think I'll get as many lights as possible, and if I can get flats and bias when back inside then fine, but I've seen an amazing photo which is just stacked lights so I'm not going to worry about calibration frames too much.

[happy-kat]

I saw, great question and you got several replies, I'm going to use them.

[Alien 13]

9 minutes ago, happy-kat said:

I saw, great question and you got several replies, I'm going to use them.

The inbuilt features like lens correction are easy to try out during the day just need two image stretches one with and one without to see how effective they are.

Alan

[happy-kat]

Lens correction only there if lens is supported which my 85mm and kit lens is but not Canon 40mm pancake

[Alien 13]

3 minutes ago, happy-kat said:

Lens correction only there if lens is supported which my 85mm and kit lens is but not Canon 40mm pancake

True but most do eventually get added or you can create your own I believe.

Alan