Cropping at original aspect:
I choose to crop afterwards, in case I don't get it framed just right (as shown above). You will gain a little flash intensity when the zoom head is in crop mode, but you could always lock that in manually.
A 55 mm f/1.8 on a crop sensor does blow out the background nicely, but not like a true 85 f/1.8 on a 35 mm sensor.
Q1. Yes- Click the padlock to close it. Aspect locked.
Q2. I don't believe it matters. My son gave me A7 raw images cropped in camera to APS-C. When I developed in LR and applied the Crop Tool, I found the image displaying full-frame with the APS-C crop margins visible. I could still go back to full-frame in LR. I would be interested to hear your findings.
Q3. Generally No, the 90mm lens has an inherent smaller DOF than the 55mm - at the same focus distance to subject. However if you move closer to subject with the 55mm to shoot full frame DOF reduces, AND perspective changes. All the variables (Focal Length, Distance to subject, Aperture, Sensor Crop Factor.) make it difficult to explain- just do some trials.
This is what I usually do, now I know for sure my aspect ratio has been locked. As far as shooting in crop mode though, what I meant about that is this; For portraits, if you take a 55mm and shoot a portrait with it, the background doesn't look that compressed, which I like. Even if it's at a good F stop. It'll be out of focus, but not "compressed" And seems to show more flaws in the person. This is why with my Canon I always used my 85mm or my 100mm. I know some who will only use a 200mm due to this type of compression that happens at longer focal lengths.
If I was to shoot in crop mode, making it 88mm, would it give me that affect? The compressed look I get from a 85mm? Or would it simply just crop it like I do in post and not really make a difference.
Sony has yet to come out with a portrait lens and I need one bad, I've been offered little jobs here and there and can't take them because I don't want to disappoint them. I'm waiting for their 90mm, because that is close the 100mm and 85mm I shot with on the 5D for portraits.
Not to same the subject here but, 'Benjamin Root Photography,' has been a great help to me on this forum. I also torn between getting the 16-35mm F/4, or the new 24mm F1.4 prime, for wide landscape shots, because landscape and hiking is where I do most of my photography.
I don't plan on actually shooting a landscape at 1.4, but if it's 1.4 that means if I stop it down to F 8 on a landscape it'll be tact sharp. But it is not a Zeiss and is only going to cost 500. On the other hand, there is the 16-35mm, still I'd shoot around F 8 or even higher for landscape, the problem is, if it's F/4 won't that mean it'll have to stop down much further than the 24mm to get a sharper picture?
I don't guess I can go telephoto, like anything over 100mm because I have the A7R. People say over 100 mm it has shutter vibration, so at 200 or 300 I wouldn't buy until the A7R ii comes out. I'm not willing to get the regular A7 ii because I really like the advantage of having all those megapixels for cropping purposes, and it just plain looks better. Which is why I took my Sony A7 back for the A7R. Everyone was saying the photo's were more impressive than the 5D Mark iii's with the Zeiss 55 1.8 vs 5D with 50 1.4L. That wasn't really the case with the A7, but when I got the A7R I seen a HUGE difference in dynamic range.
I've heard the A7 is better at focusing than the A7R, but since I switched to the A7R I have noticed literally no difference. But I don't shoot fast moving subjects.
With both cameras I notice the face detection and EYE AF is hard to get to work properly. If I let it auto focus fully It'll focus on the wrong thing a lot of times even though the green boxes say the right thing.
So, I have been putting it on a single point, keeping it at the center, focusing on the eye, and then recomposing. That's mostly how I did with the 5D anyway. I never allowed it to choose focus points for me either.
No, the lens is what determines the D.O.F. and so you'll get the same background whether it's cropped or not, unfortunately. There is really no way to make a 55 mm f/1.8 look like an 85 mm f/1.8. I mean, you could put a small extension tube behind the lens, but that's going to limit you in many other ways than it's worth.
DXO Mark and SLRGear are good places that test lenses. Personally, I would go for the 16-35 f/4 because it is more versatile. If you were shooting night photography, the 24 mm is going to let in a ton of light compared to the f/4. You loose some of your wide angle though.
I'd say you should be able you get good pictures with long lenses, unless the camera itself is lousy. Set your shutter speed to at least 1/400 for 200 mm, 1/640 at 300 mm, and so on if you're worried..
I'm glad you've posted this information here.. Good to see your thoughts on it.
I shoot a D750 as my main. I just use a single point or the new group area AF. Works nicely.