All Forum Comments
Comment by Don posted on Canon FD on Pentax body! at 25/04/2011 - 19:05
I'm pretty sure you can find a cheap rebel (check first to make sure you CAN use those lenses on the rebel) or go with a nex, nx, or 4/3s cam and buy and adaptor. Or perhaps you'll get better quality if you sell them and buy a holga... or sell them and by a pentax lens, then you can rest assured of getting fine quality.
I just gave a canon ae-1 and 50mm lens to a homeless person at a shelter. He has some interesting art pieces he's done including photos taken with disposable film cameras.
He seemed really enthusiastic about having to give up a few beers to buy film so he can go out and get better photos!
I hope he enjoys it!
I just gave a canon ae-1 and 50mm lens to a homeless person at a shelter. He has some interesting art pieces he's done including photos taken with disposable film cameras.
He seemed really enthusiastic about having to give up a few beers to buy film so he can go out and get better photos!
I hope he enjoys it!
Comment by Don posted on Canon FD on Pentax body! at 25/04/2011 - 18:44
Oggy wrote:
Don - have a look here.
The relevant part is Boyle's law which states that in a closed system, the product of the pressure and the volume are constant. Thus if you half the volume, you double the pressure.
Some very rough (fairly conservative) figures - the area of the lens is 1 square inch and the volume of the lens changes by one third between min. and max. focal length.
Assume you put the lens on at max. focal length then moved it to min. focal length, the volume would decrease to two thirds and the pressure increase by a factor of 1.5 times it's original value. You now have 1 atmosphere acting on one side of the lens and 1.5 on the other. An atmosphere is about 14.5 psi so for your 1 square inch lens, you are going to have about 7 pounds force (about three bags of sugar) acting on the lens. I am sure we would notice this.
I am convinced they have to vent but the vent system has to be quite clever.
your assumption is that they have to vent a lot the air inside them, externally is probably incorrect. Don - have a look here.
The relevant part is Boyle's law which states that in a closed system, the product of the pressure and the volume are constant. Thus if you half the volume, you double the pressure.
Some very rough (fairly conservative) figures - the area of the lens is 1 square inch and the volume of the lens changes by one third between min. and max. focal length.
Assume you put the lens on at max. focal length then moved it to min. focal length, the volume would decrease to two thirds and the pressure increase by a factor of 1.5 times it's original value. You now have 1 atmosphere acting on one side of the lens and 1.5 on the other. An atmosphere is about 14.5 psi so for your 1 square inch lens, you are going to have about 7 pounds force (about three bags of sugar) acting on the lens. I am sure we would notice this.
I am convinced they have to vent but the vent system has to be quite clever.
if the air is moving between chambers (or spaces within the lens) then the air pressure is probably greatly reduced..... depending on how you design it, you can take multiple tubes and baffles and create a collapsable/extendible tube where air moves freely between air chambers with minimal pressure and minimal air movement from outside the tubes....you just can't do it with TWO tubes.... unless those tubes have sufficient space (volume) to allow the air to compress...
i think the lens design incorporates both internal baffles/air chambers AND some air exchange from out side the system... but that overall, MINIMAL air exchange from outside the system...
Comment by Don posted on Zoom question. at 25/04/2011 - 14:07
ManixZero wrote:
My 3 lens kit is a DA15, Adaptall 24mm and 50-200 zoom.
Light and covers almost everything.
MZ
not bad choices..My 3 lens kit is a DA15, Adaptall 24mm and 50-200 zoom.
Light and covers almost everything.
MZ
my three lens kit next time I'm out will simply be the 35 2.4, 50 1.4 and 100mm.macro and maybe the 1.7 af converter, since it will easily fit in the lens pouch on my hip pack if attached to one of the smaller primes...
Comment by Don posted on A 3 Lens System at 25/04/2011 - 13:12
air does compress... it isn't like you are trying to compress water....so it would seem like a possibility that a slightly porous gasket combines with sufficient room for the air to compress (or move from one chamber to another)would still equate to a water resistant seal that allows air to seep through when there is sufficient pressure/vacuum applied... and the slight seepage would allow the air pressure to stabilize fairly quickly...
Comment by Don posted on Zoom question. at 25/04/2011 - 13:01
Algernon wrote:
Most lens mounts are only held on with 3 or 4 small screws anyway. There was an uproar in the 70's when Canon replaced their breech mount held with 4 screws with a lighter one using just 3
I use a Tokina 400mm lens that hasn't got a mount on it without any problems.
I don't think the force is all that high. If you can pick the lens up by the K mount using just your forefinger and thumb with the lens horizontal there can't be much force. If the lens gets bashed against something.... that's a different story.
I guess those morons never bothered to look at what the screws were screwed into, because if they had looked the answer would have really screwed with thier little minds..Most lens mounts are only held on with 3 or 4 small screws anyway. There was an uproar in the 70's when Canon replaced their breech mount held with 4 screws with a lighter one using just 3
I use a Tokina 400mm lens that hasn't got a mount on it without any problems.
I don't think the force is all that high. If you can pick the lens up by the K mount using just your forefinger and thumb with the lens horizontal there can't be much force. If the lens gets bashed against something.... that's a different story.
link
that is right, for most cameras, little tiny screws screwed into PLASTIC.... hence the reason I never cared that the new 35 2.4 is a plastic mount... it is at least as strong as the plastic the metal lens mount is screwed into...lol!
Comment by Don posted on Mount strength at 24/04/2011 - 22:29
Frogfish wrote:
But you live there Don .. not just visiting ! And by the sounds of it Mongolia's wide open spaces and horse riding herders are far more fun than Manitoba !
well it does have it's ups and downs... now that it is finally warm enough to break out the motorcycle... on the one hand, it is damn near impossible to scrub the chicken strips off the edges of the tires, so you wind up getting a flat spot in the middle... but on the other hand, there's 15, un-patrolled roads near my house where you can bounce the needle off the rev limiter in sixth gear..... not many places in the mountains where you can do that on a litre class sportbike....But you live there Don .. not just visiting ! And by the sounds of it Mongolia's wide open spaces and horse riding herders are far more fun than Manitoba !
Comment by Don posted on Lens Advice, please? at 24/04/2011 - 21:01
Frogfish wrote:
I have no idea why people think a macro would be a good lense to take to Mongolia. We are talking wide wide open spaces on the plains, lakes, rivers, people for sure, horse-riders, congested chaotic cities / towns and possibly temples.
If it were me I'd be taking a Sigma 10-20 (or similar Pentax / Tamron), your 18-55 and your 50-200. And you've got it covered. You may also need a wide low light lense (I'd suggest one of the Sigma line-up of 24/1.8 or 28/1.8 (which is a macro too !) or 30/1.4) as you will be in plenty of poorly lit environments, possibly even inside a yut. Take lots of batteries, a CPL filter and SD cards plus your tripod.
I live in Hell....I mean Manitoba. We have farms bigger than some countries. You see one farm you've seen them all.I have no idea why people think a macro would be a good lense to take to Mongolia. We are talking wide wide open spaces on the plains, lakes, rivers, people for sure, horse-riders, congested chaotic cities / towns and possibly temples.
If it were me I'd be taking a Sigma 10-20 (or similar Pentax / Tamron), your 18-55 and your 50-200. And you've got it covered. You may also need a wide low light lense (I'd suggest one of the Sigma line-up of 24/1.8 or 28/1.8 (which is a macro too !) or 30/1.4) as you will be in plenty of poorly lit environments, possibly even inside a yut. Take lots of batteries, a CPL filter and SD cards plus your tripod.
My macro gets used way more often than my wide angles around here... the closer you look, the more beauty you find... around here anyways, a close up of a prairie crocus is way more interesting than the wide open expanse of prairie you found it on....
Comment by Don posted on Lens Advice, please? at 24/04/2011 - 20:49
I would take the 12-24, the 50 1.7, and 105 sigma and spend a few extra bucks an a k5....
Comment by Don posted on A 3 Lens System at 24/04/2011 - 18:42
yeah i also clicked on a couple links there....
looks like an apsc evil to me.....
edit, wrong link to wrong camera...sorry, no photo...
looks like an apsc evil to me.....
edit, wrong link to wrong camera...sorry, no photo...
Comment by Don posted on there are still rumours about Pentax Evil Cameras.. at 24/04/2011 - 18:32
haha don amazing story.
the A1 looks way too complicated for me, I dont use my camera on full manual mode (unless I have played with the settings first then keep testing), but realistically I dont think I could get a decent shot on a film camera... which is a shame! I am very tempted to use the 135mm f2.5, even the 50mm f1.4mm has a dot in the middle that moves depending on whether you're in focus or not, i havent seen that on a pentax lens but it looks useful!!
I dont think the rebel would work, I think I might buy a film and give it a go, just for the "feel" of it, and then it'll end up on ebay and I guess I'll get a Pentax lens
set the iso on your kx to match the film in the canon, then take the photo first with your kx, then read the info on the shot on your kx, then transfer those settings into the film camera...