Watching Over

by Vian Esterhuizen

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96,730 reputation
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bio website mattgrum.com
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visits member for 4 years, 4 months
seen 7 hours ago

7h
comment How does autofocus deal with the time to change aperture and raise mirror?
@AlecTeal I'll see if I can dig out some Canon AF system white papers, I remember them talking about coping with objects that stop / start and move erratically which implies nonlinear motion estimation.
18h
comment Comparison of DOF between a 30mm f/1.4 and a 35mm f/2 lens
When you match the framing by moving the 35mm further away to compensate for the narrower FOV total DoF changes to 0.32m
Jan
23
comment Technical book or resource (non-creative)
You wont find good answers to all these questions in one book, as they range from the trivial (design of lens hoods) to basic optics (origins of chromatic aberration / limitation of single element lenses) to very complex (causes of onion ring bokeh, something I've yet to see a convincing explanation of from anybody, but may involve the construction techniques of aspheric elements, which is itself a high level topic)...
Jan
21
comment Is there a correct way to swap lenses?
@Szabolcs There's a difference between dust and sand, for sure, having had a lens mechanism ruined by a single trip to the beach my advice in that area would be "don't take your camera to the beach!" But if you really want to do so then you'd be well advised to change lenses in complete isolation, in your car, or inside a bag at the very least.
Jan
21
comment Is there a correct way to swap lenses?
@ChrisH I've always done the method of getting the new lens on immediately after the old one comes off, on the basis that it's easier to brush dust of the rear element than it is to remove it from the camera body. Either method is acceptable though.
Jan
21
comment Is there a correct way to swap lenses?
It really depends on what your priorities are, but dust will happen. In my opinion you're better off having a cleaning strategy, and then change lenses as often as you need to get the shot, rather than trying to minimise how often you change lenses.
Jan
21
comment Is there a correct way to swap lenses?
With regards to 4, there are scores of people, myself included who have been changing lenses with the camera on for decades. I have yet to hear of a single case of this resulting in any damage, if there was a risk there would surely be at least one case.
Jan
20
comment Is it risky to change lenses in the cold?
@JonStory I always use a bag these days. Neither the lens nor camera body are airtight in general, so the interior is exposed (to an extent) as soon as the camera is indoors. Also I've seen condensation form very quickly on the lens front element / camera LCD screen. This water can easily run through joins in the camera/lens if it's they're not weather sealed.
Jan
15
comment Shooting full manual during an event or function
@TiaanRossouw Fluorescents do horrible things to your photos with fast shutter speeds, see: photo.stackexchange.com/questions/4115/…
Jan
14
comment Which is the application used for this photo with glow around dark things? I saw many pictures like this on instagram, but nobody answers
You're asking what application was used for these shots so you can avoid it at all costs, right?
Jan
13
comment How to take this group portrait with faces in profile only lit from the side they're facing?
sorry, should have stated it needs to be dark if you're going to do it outdoors! The thing about black sheets is they are not 100%, i.e. they reflect some light back. The closer they are the more they reflect back, the further away they are the bigger they must be. However, if you get the background far enough away it doesn't have to be black (or a sheet), hence the naturally surroundings will show up jet black, provided they are far enough away.
Jan
8
comment Is there a flash system that will work with for both Canon 5DMKIII and Sony A7MKII?
I pretty sure none exist with TTL functionality (camera/flash communication protocols differ), in any case I don't think you'd want to use the same flash for both a 5D and A7, I have used a Canon 430EX on an A7 (in manual mode) and it balances very badly, plus the whole thing will hang upside down if you use the neck strap. I think you need a smaller, lighter flash for an A7, thus you should get one that is compatible with Sony TTL (I haven't looked into specific options yet).
Jan
7
comment How can I set my Canon 5D Mark II to JPEG only?
@DetlevCM When you have limited storage for whatever reason not having the RAW means you can store many more JPEG frames. I did this this summer on a trip after picking up a Sony A7R, I have a huge number of CF cards but very few SD cards (I wanted to evaluate the camera before investing in cards). I shot RAW only rather than RAW + JPEG to save space. Most of the time I shoot RAW + JPEG for convenience as storage is usually not a problem.
Jan
7
comment How can I set my Canon 5D Mark II to JPEG only?
RAW + JPEG is the way forward.
Jan
5
comment Why don't sensors on satellites and rovers degrade as quickly as DSLRs on the space station?
@jdlugosz because a camera is more than just a chip holder! Using a DLSR is much more convenient than NASA designing their own cameras for astronauts to use. Photos taken with DSLRs are not part of core ISS missions, they are just supplementary, the same is not true of the Mars rover cameras etc.
Jan
5
comment Do flash guide numbers assume some amount of ambient light built-in?
For many the main difference between the 430EX and 580EX is the power, features are broadly similar (600EX-RT is effectively the "next generation" unit, I expect a 450EX-RT or similar released soon). I do own both the 430Ex and 580EX (which currently has a broken hotshoe, but should be able to fire it using the PC port) I'll do a quick comparison when I get a chance!
Jan
5
comment Is it possible to get smaller aperture with diaphragm in front of the lens?
DoF increase will depend principally on the size of the hole, and is not determined or really connected to the amount of vignetting that results. Again, I'm not saying this is a good idea, just that it is possible to control depth of field by adding a filter to the front of a lens.
Jan
5
comment Do flash guide numbers assume some amount of ambient light built-in?
@mattdm Wehn the (theoretical) difference between Canon's midrange 430EX and brand new top of the line 600EX is less than a stop, being within a stop is not saying much at all!
Jan
5
comment Is it possible to get smaller aperture with diaphragm in front of the lens?
Vignetting is not the only thing you will get, you will also get increased depth of field as intended. It's not a good solution by any means but it will work.
Jan
5
comment Do flash guide numbers assume some amount of ambient light built-in?
@dpollitt I doubt manufacturers test the flash to come up with the GN initially, they will set out to design a flash with GN of say 43 (according to what market research suggests will sell) and then calculate the power required. I doubt any of the commonly available flash units are actually as powerful as they claim to be.