Why use 25p over 30p in HD?
 

Just wondering what peoples thoughts are on using 30P or 60i as a standard for HD in the UK (if you're not going out to broadcast)?

Doesn't it make sense to use 30p/60i HD, given you get those extra frames and especially with undercranking? What am I missing?

Paul.

What happens if you want to downconvert to SD PAL? Using a 25/50 framerate would work out much more easily for you.

Cheers - Yes I had considered that but most of my projects end up on the web or played back in HD from Powerpoint etc.

Just wondering if there's any other reasons I would stick to PAL?

If you never expect your video to end up on a standard definition television, I don't expect the frame rate to matter much for anything beyond aesthetics.

You need to use 25P or 50i to sync to your power line frequency of 50hz. Under certain lights, the odd multiple of power frequency vs. frame rate will cause issues.

-gb-

Thanks Greg - I presume you're talking about flourescent lighting predominantly?

Presumably this would also apply to these new low energy bulbs that are becoming popular these days too.

I think this may certainly be the case with the cheaper (non integrated) CFL's as these do not have a high frequency ballast (I believe) - the expensive (or two part lamps) will have a ballast and will possibly(?) operate at higher frequencies.

Either way, they're orrible lamps! ;)

Yes, but keep in mind that even a tungsten bulb is being energized/de-energized at 2x the line frequency. If your frame rate is an odd multiple of that, you could have some brightness/color fluctuation as your camera exposes each frame at a different point in the power line wave cycle.

-gb-

Sure - but tungsten is going to react much less compared to flourescent isn't it?

Hi Guys,

These are interesting thoughts on the AC current frequencies of light but I wonder: I used the shutter in 70 or 85 Hz regularly to shoot CRT computerscreens in the past and it never occured to me that that change of shutterspeed led to weird effects with lamps.

What should you see in the VF with different AC freq.?

Standard fluorescents will be more of a problem for sure, unless they have high frequency ballasts. Not likely in the average office scenario though.

-gb-

You'll also have problems with many industrial lights such as sodium and halide discharge lamps. The types of high bay lighting in many factories and warehouses runs at 50hz.

I use 25p. Most of my web clips run at 25p to save bandwidth (compared to 30p). 25P is slightly less compressed than 30p, although I cant see a difference at 35MB (I can at 25Mb).

Changing the subject completely - Do you always use 25P regardless? - I'm used to doing everything at 50i in the old SD days with my 570 and de-interlacing at final compression stage. Always had excellent results with pans and zoons etc.

I'm still not sure I like the motion effects with 25P - seems a backward step to me! I don't go for the cinema look either very often. I do like a smooth and seemless result :)

I guess the biggest benefit of editting progressive (for me) is for graphics and titles etc - they never do too well when de-interlaced. I used to often run a progressive project and import the filmed interlaced footage into it and set it to de-interlace. I also have regular jobs where I composite a chroma-keyed presenter onto motion graphic or computer screen capture background and mix between them with various other effects. These types of project are ideal for progressive footage of course.

how does 24p deal with these issues as opposed to 30p?