Would anyone like to have some G lenses that are APS-C size

[Greg Beetham]

Yeah Henry I agree, the wide aspect with APS-C is not wonderful, thing is, with FF wide angle is so effortless by comparison, FF easily blows APS-C away shooting interior spaces especially, you only have to look through the VF of a FF camera (35mm film will do) at 17mm inside a room and then put the same lens on an APS-C cam, massive difference. That's one reason I'd like an A850...the other is FF is superior at scenic shots, I don't think APS-C would ever challenge FF in that area, so I'm secretly lusting after an A850, or A900, either one would do very nicely for that.
Greg

[bfitzgerald]

I have a hard time believing you'd be satisfied with any of the compromises of getting a FF DSLR under £1000. You're hardly satisfied with any of the APS-C offerings under £1000.

Time will tell. I don't see it as unrealistic to hit that price point for FF shortly. I can live with a plastic body, have done with the 7 film...You have misquoted me though..
I'm hardly satisfied with any of the current "Sony" offerings under £1000, big difference I could see myself using a couple of mid range bodies from other makers, I'm not responsible for Sony and their inability to provide adequate products for their target market lol

Back on track, FF has it's pull for wider angle, of course I am not a tele shooter much, so I don't really find APS tele appealing, I am sure some would.

[Dusty]

It's only a matter of time before we get a sub £1000 FF body, and I'd hate to have a load of lenses that are APS-C.

I have a hard time believing you'd be satisfied with any of the compromises of getting a FF DSLR under £1000. You're hardly satisfied with any of the APS-C offerings under £1000.

The electronics - Sensor being key here- is what's adding most to the cost. When the electronics package, including the FF sensor, gets down low enough, we'll see it. Then they can add value (and cost) by adding back in all the features they've been stripping out to save a buck or 2.

Dusty

[bfitzgerald]

I have no idea on margins for FF models, or even higher end APS-C. I suspect that they are higher than most expect.
Take a retail A850 for around £1500, out of that you have 17.5% VAT adding to cost. Manufacturer profit, retailer profit margin. I bet the actual production cost for this camera is not as high as some might think. And I doubt the sensor is a huge cost on it's own, makers would want you to "believe that"

Worked with pc's for long enough, nobody could have imagined how low cost a pc is nowadays, go back over a decade, they were far from cheap.

[YorkieBen]

Yes the 70-300G is another Sonyfied 'G', not constant aperture and not particurlarly fast either, the one thing Sony didn't forget to do was adjust the price accordingly to suit the name, I think I must have subconsiously not considered these as proper G lenses in the traditional Minolta sense, the one who originally made G lenses what they were.
When you think about the Sony 70-300G, if they had made it a 100-300 instead they surely would have been in striking distance of constant aperture (like the Sigma 100-300 f4 APO), say f4 or f4.5 without making it overly large and heavy. Although the Sigma 100-300 f4 APO is reputed to be a fair lump (I've never handled one), and quite a good lens, Sony probably wanted to have something different enough to be attractive/versatile enough for people to justify buying instead.

the sigma 100-300mm f/4 is twice and heavy and alot bigger than the 70-300mm G, and alot more expensive!

[Greg Beetham]

the sigma 100-300mm f/4 is twice and heavy and alot bigger than the 70-300mm G, and alot more expensive!

I'm pretty sure most know (like I said, it's a lump) that the FF Sigma is large and heavy...Sigma (can't find the APO version) 100-300 (D) EX DG IF f4 is 1.4Kg and has a 82mm filter and cost is $1200 B&H as against the Sony FF 70-300G f4.5-5.6 is 0.76Kg 62mm filter and cost is $850 B&H....
What the object of the exercise is, (this thread), is to try to imagine what could be done by re-designing these lenses and others for a much smaller image circle in terms of weight saving etc. And I was saying, (if you read what I said) that if the Sony 70-300G was re-designed from the ground up for APS-C format then Sony might have been able to make it a constant f4 or f4.5 without incurring any (or much) increase in weight....and as an added bonus it would then become a REAL 'G' lens.
Greg

[David Kilpatrick]

It's not the image circle which determines the weight and size - it is the focal length and aperture. You can not make a 300mm f/4 without using 75mm of actual glass diameter. If that is in a zoom, you do not need 75mm of physical aperture opening, as the iris is positioned to do this 'virtually' aided by a positive front group. A typical actual iris in unlikely to be larger than 40mm in diameter, which means the front group must have a focal length of about 150mm and the rear zoom group must incorporate a negative power of 2X before the exit group focuses the image on the sensor plane.

It's the final rear group which can be reduced in size for APS-C versus FF, and this is not really the heavy part of the lens.

David

[Greg Beetham]

T-stop transmission per square mm at the sensor plane should remain the same for a given aperture, logic says that as you reduce the projected field (image circle) it also brightens, how do they make small tele lenses for small sensors then? going by that reasoning every lens would be of a similar size regardless?
Greg

[David Kilpatrick]

T-stop transmission per square mm at the sensor plane should remain the same for a given aperture, logic says that as you reduce the projected field (image circle) it also brightens, how do they make small tele lenses for small sensors then? going by that reasoning every lens would be of a similar size regardless?
Greg

Logic says that if you reduce the image scale as well as the projected field, it brightens! Sure. That's how the 7.2-50.6mm f/2.8-3.5 zoom was possible on the A2etc - a '28-200mm' relative to the image field. And because the reverse applies, that's why teleconverters (which enlarge the image circle and scale) lose you a stop or two.

But if you simply reduce the image circle, you do nothing with brightness at all. Fit a lens hood which is too deep, and you can reduce the image circle - certainly won't brighten your pic.

Don't confuse this with wide-angle lenses, where having a smaller image circle will reduce the overall size of the lens a lot - and so will having a smaller aperture. With a telephoto or tele zoom, the minimum size is simply dictated by the formula for the aperture. 300mm f/4 = 300/4 = 75mm so it's physically impossible to make any 300mm f/4 lens which is less than 75mm in diameter. In fact, to avoid vignetting and fit the mechanical parts of the barrel, the front filter rim will usually need to be 82mm for a 300mm f/4 but 77mm is possible.

And as for the length, that depends entirely on telephoto construction. A single meniscus (simple lens) 300mm f/4 will be 300mm from the sensor plane at infinity, no matter whether it's made for 2/3rds video or 6 x 6cm Hasselblad. Anything shorter is a result of using a negative rear group and a shorter focal length front group (telephoto construction).

David

[Greg Beetham]

Well okay, how about considering it in reverse then, sortof, you have a lens rated at f:whatever on a tube, the tube has a correction factor for the amount of extension (light in the projected image circle has dimmed because the correction factor changes the base f-rating of the lens for exposure calculations).
Why has it dimmed? was it because you now have a lens that is x much longer than before? or the one I like best, the projected image circle is now much larger than before and the same amount of light is now spread over a much bigger area.
If you take the above as true then the reverse should apply, if you take a telephoto lens and just replace the rear group with a re-designed group (not a complete re-design...yet), so that the available light (whch has not changed) is projected into a much smaller image circle than before, that light should be more concentrated and brighter....
There is an anomaly in the way lenses are descirbed on APS-C anyway...how does, say a FF 300mm f4 become a 450mm f4 once fitted to an APS-C camera? when it still has the same objective lens as before ie. 75mm (or as you say 82mm in reality)..whatever, the thing is, too achieve that performance (450mm f4) it should have an objective lens of 112.5mm...correct?
Greg

[David Kilpatrick]

Greg, if you reduce the scale and increase the brightness of the image you just get a shorter focal length.

That's why the Sigma 50-150mm f2.8 for APS-C is smaller than the Sigma 70-200mm f2.8 for full frame.

But it is not a 70-200mm f/2.8, and they do not make a 70-200mm f/2.8 for APS-C because it would be just the same size as the full frame one, and much less use.

If you want practical examples, the Sony 50mm f/1.8 for APS-C is widely criticised because it's no smaller than the original Minolta 50mm f/1.7 - it just doesn't cover full frame, which is stupid. But Sigma's 30mm f/1.4 for APS-C is much smaller than their 28mm f/1.8 for full frame, mainly because of the size savings possible if you make a short focal length lens have a smaller angle of coverage. Same for Sony's 30mm f/2.8 macro for APS-C, and for some 'pancake' type lenses like the 20mm f/1.7 Panasonic 4/3rds.

It simply doesn't apply to long lenses. End of story. The reduction in size holds good with identical angle of view and aperture but smaller format. It can not happen to any significant degree with identical focal length and aperture but smaller format. That is, with any lens other than a retrofocus design (shorter than approx 35mm focal length on full frame) or a retrofocus zoom (wide to tele zoom).

Thus you will find that an 18-200mm Tamron for APS-C is possible, and relatively small, but it's not SO much smaller than the 28-300mm similar lens for full frame. But if you tried to make an 18-200mm for full frame it would either prove impossible, or be massive.

David

[Greg Beetham]

Ok I've got it, (I think) the only way to actually get a smaller lens on APS-C is to design the lens to have the same equivalent performance. So you could design a 200mm f4 for APS-C and it would have the same image scale magnification and angle of view as a 300mm f4 on FF....correct?
Greg

[David Kilpatrick]

You've got it. The 135mm f/2.8 AF lens used on APS-C is equal to a 200mm f/2.8 on full frame - and it's a much smaller lens.

David