40D techie questions

johnt

johnt

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John
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Hi all,

Well I have just purchased a new 40D (the cashback deal did it for me!) and I am very pleased with it. I do however have a few questions and if anyone knows the answers then I would appreciate it:

1. Do you leave highlight tone priority on all the time, and if not why not?

2. Why is iso 3200 hidden away in the menus? Does enabling this somehow effect other aspects of the cameras performance?

3. Why is the file size on average larger than the 400D even though it is still 10M pixel?

Thanks

John
 
With Highlight Tone Priority selected you lose the ability to use ISO100. HTP starts at ISO200. So I usually use it but when I need ISO100 I'll switch it off. In fact with HTP selected you can only select 200-1600 so 3200 is not available.

ISO3200 is not a "real" setting. The sensor is not any more sensitive than at ISO1600 however the camera boosts the the exposure in its software I believe.... Someone else may be able to provide more info on this though. Also at ISO3200, there is a fair bit more noise than at any other ISO and there may be a reduced dynamic range.

File size relates to many things. Check out changing even the ISO. Higher the ISO, less images will be available on your card!

Are you comparing one file type? With RAW images, the main difference to file size will be that the 40D produces 14bit files compared to the 400Ds 12bit.
 
I've read somewhere that Highlight Tone Priority can induce more noise in shots. Having said that, I have it set nearly all the time, and can't say I've noticed any noise issues.
 
Personally I leave the highlight tone priority off as I rekon it does leave the image with more noise and also I shoot RAW which it does not affect, plus bit of a sales thing IMO. 3200iso really is noisy and I could well believe what EOS_JT said about it not changing the sensor sensitivity and the levels being changed by the software which would exsplane the loss in dynamic range. File size is bigger I would rekon because its a different sensor?
 
file size - difference between 12 bit and 14 bit images - extra information has to go somewhere. Are jpg files similar size between 400D and 40D?

I've thought highlight tone leaves noise. I tend not to use it as a lot of the work I do apart from motor racing is at fairly high ISO anyway and the possibility of extra noise isn't something I want.
 
Thanks chaps some good answers there.

To answer your question, I am shooting everything raw not jpeg, and the average file size is about 2-3MB larger than a comparable 400D.

interesting about the 3200 iso, i will probably not bother with this then!

just thinking about it, I wonder if highlight tone priory is just a form of automatic exposure compensation. It makes sense because if you cannot use iso 100 the camera is using the iso for the compensation. If you had access to iso 100 the camera has nowhere to go.

I did some test shots at the weekend of horses in a sand school. This was tricky as the horses were brown, the sand almost white and the riders skin/shoulders exposed on a very sunny day.

With highlight tone priority turned on for all shots I was still getting some blinking highlights on the preview in the sand and on the skin. Looking at the file at home on the computer though I was able to rein back the highlights and there was still detail not completely blown. I'm not sure if this because of the file being raw or because of the highlight tone priority. More tests needed!

The only thing I can say is that I did not detect any noise in the pictures, auto iso chosse 400 and that worked well.

I would welcome any further comments on your experiments.

John
 
Don't forget your file size is also determined by white space. Lots of white space equals smaller file sizes. Maybe you are shooting different pictures? I have used the ISO 3200 and was surprised how good it was all things considered. I shoot RAW and JPEG. I do this so I can quickly tinker with the JPEGS then if it looks good be more serious with the RAW files.
 
johnt said:
Just found this interesting expalnation of highlight tone priority:

http://www.bobatkins.com/photography/digital/canon_eos_40D_review_6.html

Looks like it's worth just leaving it turned on.

Also, reading the rest of the review, it appears that it's best to leave high iso noise reduction on unless you want to use the fastest frame rate.
Click to expand...

That HTP thing tends to make the shadows rather noisy though (so I've read)

Ally said:
To be honest you just can't beat a properly exposed file in the first place.
Click to expand...

Can't argue with that....
 
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