Canon 40D Live View limiting magnitude

[Mark]

A little experiment I did tonight to find the actual limiting magnitude of the 40D's Live View. Using my 8" SCT @ f/6.3, I started with a mag 2 star and went in (roughly) half mag steps down to where I could not see the star in the main live view window.

I found approx mag 5.5 to be the limit in the main window. Using the zoom mode I was able to see better than mag 6 but that is where I stopped.

I then slewed to a mag 4 globular cluster but I was unable to see the object in either normal or zoom mode in the live view. I can only conclude that low surface brightness objects are going to problematic with respect to using live view for focusing.

Therefore unless there is a mag 5 to 6 (approx) or brighter star associated with a DSO, live view will not help me focus.

I would like to here form other 40D users with different types of scopes (newts or refractors) to see what results you are getting.

I would also be interested in whether anybody has had any success with a parfocal eyepiece setup for their dslr?

Cheers,
Mark

[rogerg]

Mag 6 @ F/6.3 is pretty good I think. That'd be good enough for my uses anyhow.

Thanks for the report. :thumbsup:

[citivolus]

Does the ISO setting impact this sensitivity at all? Also, there is an option to simulate the actual exposure in live view mode. If you use live view + a long exposure, does it intensify the output somewhat? I just did some very preliminary testing of these settings, and found that ISO did not seem to make a difference, and that exposure times longer than about 1/10 of a second were not adding anything to the LCD brightness. It would seem that the default setting of automatically adjusting the LCD brightness may in fact turn out to be the most sensitive.

It would be worth checking these settings on something more appropriate than my wall, though :)

[Mark]

Not in "LCD auto adjust" mode. During last night's testing, I set ISO from between 400 and 3200 with no apparent difference to the live view image




Aha! Thanks for reminding me. I had completely forgotten about it. This I did not try. Hmmm. I think that is worth pursuing tonight. :thumbsup:

Preliminary testing on my wall in a darkened room: at ISO200, nada. At ISO3200, woohoo! I see bricks. This could work.

Thanks!
Mark

[Mark]

Using Live View exposure simulation had no effect on low surface brightness objects. I tried viewing a mag 4 glob in this mode with ISO set to 3200. I used both the camera LCD (set to lowest brightness) and a laptop. Neither method allowed me to view the DSO in Live View using an 8" SCT @ f/6.3.

With respect to my scope, my previous conclusion still stands: Focusing Low surface brightness DSO's using Live View will be problematic.

Perhaps a larger aperture scope combined with a faster f ratio would provide better results.

I'm disappointed. :(

Mark

[citivolus]

Thanks for checking that, Mark.

I wonder about USB mode once the API is out there. I would think it would be possible to boost the gain substantially while focusing, at the expense of noise.

Eric

[Mark]

Agree. I live in hope. Even if there's no solution to this problem, I'd like to see an improved software interface for astro use other than the EOS Utility.

Mark

[citivolus]

I've been doing some experimenting with interesting results.

A couple of nights ago I noticed I could see Sigma Octantis with live view and the 90mm refractor. Being that I'm not that good with the faint stars in that area visually, it got me thinking...

I've now got a *free* digital polar scope/reticle courtesy of the 40D, Eos Utility, Cartes du ciel, and a freeware app called "transparent window". How?

-Shoot an image of the polar region with the scope to establish a field of view. Theoretically this image could be of any sky region that you can find later on in CDC.

-In Eos Utility, find the size (x * y) of the live view preview. I used a screenshot and measured it in Photoshop, other apps would work for this as well.

-create an image with that resolution. Content not important, but CDC has to be able to open it, so a simple bmp is good.

-Import SCP image into Cartes Du Ciel, tinker with it till I figure out the exact field of view.

-Import live view sized image into CDC

-"Find" the SCP using CDC, using the field of view calculated above, and create and save a screen shot.

-Open the screen shot in any app, including the windows viewer.

-Start "transparent window".

-Start Eos Utility, launch live view

-Bring up the window displaying my finder chart, over top of the live view. Slide transparency to around 50%, position the image over top of the live view image. Slide transparency back to 100%

-Bring the live view image back in front, slide its transparency down to a usable level.

-Enjoy your software reticle!

For $95 USD you can get DSLR Remote Pro which handles the live view and overlay component, but, well, it isn't free :) You'll still have to create suitable image files to use as your overlays. There are lots of potential applications here, including composing DSO shots.

I've currently got one image of the SCP to use prior to initialising goto on my mount, and one of Sigma Octantis at the centre for use in the polar alignment routine.

I'm also tinkering with the Canon SDK to see if I can come up with an app of my own to do this with selectable gain for live view, and alternate overlay techniques. We'll see where that ends up. I've noticed noise in the live view display in low light when using the PC mode, so it may not be very boostable.

Eric

[RB]

I'm not sure if live-view works the same on the 40D as with the 20Da that I use but when I focus I just focus on any relatively bright star, lock in the focus and then go over to the object I want to image.

[Tamtarn]

We do the same Andrew, and use live view to focus on a bright star, lock the focuser and then go to the object and compose the image.

Once the image is composed we tun off live view and set the canon program on the laptop for an auto run on multiple exposures.

[dugnsuz]

I've found I get the best focus by finding a not-so-bright star (sorry can't give you Mag figure), then the star 'disappears' from the live view window either side of the focus sweet spot. Seems to work the best for me - if I focus and lock on say Sirius, I find that the brightness of the star blurs that sweet spot a bit.

Cheers
Doug:thumbsup:

[TechnoBill]

Hi All,

I recently got a 40D as well. I have been using it with an LX200 8" SCT and 6.3 reducer. I am very new to Astrophotography.
I have found that Exposure does slightly affect the sensitivity of the Live View but Iso does not. (I pump it through to my laptop and use the EOS utility).

I havent had a chance to play around much yet, but I also hooked the video out from the camera to my TV and live view works through the video feed as well (although there are a couple of display overlays that cannot be turned off). Still, by using a cheap $15 USB vid capture I was able to use video capture programs on my laptop to display live view. This may give us more options as there may be Video capture programs out there that can intergrate the video frames to boost the image.

I guess it depends what you want to use it for. I would like this feture just to help when positionaing the fainter objects, or for multiple people to see an object on screen etc.

Regards
TechnoBill

[tornado33]

Heres a question, can live view be used as a video capture device for planetary imaging?
Scott

[Mark]

It can...sort of. Live view increases CMOS sensor noise the longer it is 'on' and therefore would be a limiting factor, plus I' don't know what the long term affects of having live view on for extended periods would be.

I tried it. My opinion? You can't beat a webcam or a planetary imaging camera for this purpose. ;)

Mark

[citivolus]

I would also suggest a different tack for capturing live view. I've been working with the programming API, and the individual live view frames are sent to the PC over USB as a JPEG file. You could stream those individual frames to disk fairly easily for use in Registax or the like. I'll see how easy it is to set something like that up.

Note that Live View is reduced resolution. The capture resolution of full frame is 1024x680, with a lower final resolution when 5x and 10x zoom are active. I think you gain access to individual pixels at 10x zoom, but I have yet to confirm that. I'll also try to verify the JPEG compression level; hopefully it is very low. I'll try to have a look at this soon, but my schedule is a bit crowded right now.

Regards,
Eric