300 GM with 2X vs 400-800 for BIF?
p.1 #1300 GM with 2X vs 400-800 for BIF?
I have both lenses and have been very happy with both. On semi-static subjects like Bison, Big Horn Sheep and Coyote, I find the 400-800 to be great as well as bird on stick. I have a very limited number of outings with the 400-800 for BIF, but my results seem strange. While shooting on an A1 II, it seems like the 400-800 at 800 finds the birds faster and maybe holds better than the 300 GM with a 2X TC on it. But when I look at cropped images, the images from the 300 GM with 2X look much better.
Is this just an outlier based on limited attempts with variable lighting conditions and therefore ISO?
For shooters who do a lot of BIF and use both lenses, do you agree that the 400-800 seems to focus a bit faster and hold better than the 300/2X? Do you get better images from the 400-800 or does the 300 GM with 2X still outperform it despite only being at 600mm and lagging a bit in AF speed?
Is this just an outlier based on limited attempts with variable lighting conditions and therefore ISO?
For shooters who do a lot of BIF and use both lenses, do you agree that the 400-800 seems to focus a bit faster and hold better than the 300/2X? Do you get better images from the 400-800 or does the 300 GM with 2X still outperform it despite only being at 600mm and lagging a bit in AF speed?
Jul 17, 2026 at 10:54 PM
p.1 #2300 GM with 2X vs 400-800 for BIF?
Does this also happen when your 400-800 is at 600mm and both are shot at the same aperture?
Jul 18, 2026 at 12:17 AM
p.1 #3300 GM with 2X vs 400-800 for BIF?
I have very limited data to work from. I don't do a lot of BIF in summer, but happened to be doing some on Bobolinks this summer. I would like to sort out what to take for a fall/winter trip. I have seen lots of reference in the 100-400 f4.5 GM talking about the AF speed of the 300GM with 2X TC vs 100-400 with 1.4X, but not much comparing the speed accuracy to the 400-800
Jul 18, 2026 at 09:23 AM
p.1 #4300 GM with 2X vs 400-800 for BIF?
Would you be able to post examples of shots that you consider substandard?
I'd consider it very interesting to see if it looks like haze, missed focus, hand shake etc. or simply lens sharpness as the culprit.
I'd consider it very interesting to see if it looks like haze, missed focus, hand shake etc. or simply lens sharpness as the culprit.
Jul 18, 2026 at 12:06 PM
p.1 #5300 GM with 2X vs 400-800 for BIF?
Let me give all the caveats so I don't get called a moron!!
Shot on different days. Small birds with huge crops. It is a protected breeding area so you can't leave established trails to get closer. I know the "other factors' are likely to be as big as or bigger than the lens differences, but that is why I am asking the question.
Here are 3 from each
300 with 2X
400-800
300 with 2 X
400-800@800
300 with 2 X
400-800@483
Shot on different days. Small birds with huge crops. It is a protected breeding area so you can't leave established trails to get closer. I know the "other factors' are likely to be as big as or bigger than the lens differences, but that is why I am asking the question.
Here are 3 from each
© Billsnature 2026
300 with 2X
ILCE-1M2 FE 300mm F2.8 GM OSS + 2X Teleconverter lens 600mm f/6.3 1/3200s 1250 ISO 0.0 EV
© Billsnature 2026
400-800
ILCE-1M2 FE 400-800mm F6.3-8 G OSS lens 800mm f/8.0 1/2500s 12800 ISO 0.0 EV
© Billsnature 2026
300 with 2 X
ILCE-1M2 FE 300mm F2.8 GM OSS + 2X Teleconverter lens 600mm f/5.6 1/2500s 1600 ISO 0.0 EV
© Billsnature 2026
400-800@800
ILCE-1M2 FE 400-800mm F6.3-8 G OSS lens 800mm f/8.0 1/2500s 12800 ISO 0.0 EV
© Billsnature 2026
300 with 2 X
ILCE-1M2 FE 300mm F2.8 GM OSS + 2X Teleconverter lens 600mm f/5.6 1/2500s 3200 ISO 0.0 EV
© Billsnature 2026
400-800@483
ILCE-1M2 FE 400-800mm F6.3-8 G OSS lens 483mm f/8.0 1/2500s 12800 ISO 0.0 EV
Jul 18, 2026 at 01:21 PM
p.1 #6300 GM with 2X vs 400-800 for BIF?
Different shooting conditions and different methods of processing, I would say. It seems that the posted images taken with the 300mm plus TC are larger crops and a tad oversharpened relative to the others.
Jul 18, 2026 at 01:40 PM
p.1 #7300 GM with 2X vs 400-800 for BIF?
Thank you very much for sharing your images. I think they are overall beautiful, it is hard to get small birds in flight in general. I like the wing poses.
The 400-800 images are ISO12800 with the subject relatively small in the frame at even 800mm. I think you should give it another chance in better conditions.
Of course it would be valid to say that you were at ISO 12800 because of the f8 limitation of the lens, but that is another consideration.
The 400-800 images are ISO12800 with the subject relatively small in the frame at even 800mm. I think you should give it another chance in better conditions.
Of course it would be valid to say that you were at ISO 12800 because of the f8 limitation of the lens, but that is another consideration.
Jul 18, 2026 at 02:07 PM
p.1 #8300 GM with 2X vs 400-800 for BIF?
From my perspective, at such crop level, the light hitting the birds makes a big difference.
Seems as for the 4-8 exemples, bird is in the shade, while for the 300 they have good light hitting them, which makes all the details to pop more.
Seems as for the 4-8 exemples, bird is in the shade, while for the 300 they have good light hitting them, which makes all the details to pop more.
Jul 19, 2026 at 01:23 AM
p.1 #9300 GM with 2X vs 400-800 for BIF?
I don't own either lens, but from what I have read from those that do, I doubt very much that the 400-800 at 800mm & f8 would find and track better than the 300mm with 2x at f5.6.
The images you posted are absolutely useless for making credible comparisons because there are so many different variations in the shooting conditions.
Jul 19, 2026 at 08:38 AM
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p.1 #10300 GM with 2X vs 400-800 for BIF?
#2 & #4 appear to be the same image. 
Jul 19, 2026 at 08:42 AM
p.1 #11300 GM with 2X vs 400-800 for BIF?
There is a significant noise difference between ISO 1600 and 12800. That noise eats edge contrast.
Jul 19, 2026 at 08:51 AM
p.1 #12300 GM with 2X vs 400-800 for BIF?
Imagemaster wrote:
#2 & #4 appear to be the same image.
I don't think so. There is the grey thing (it is highly blurred but I would guess a tree trunk) in the background on the left for #2 that isn't there for #4. But I would bet they are the same bird from likely the same burst, so obviously very related shots.
#2 & #4 appear to be the same image.
I don't think so. There is the grey thing (it is highly blurred but I would guess a tree trunk) in the background on the left for #2 that isn't there for #4. But I would bet they are the same bird from likely the same burst, so obviously very related shots.
Jul 19, 2026 at 09:56 AM
p.1 #13300 GM with 2X vs 400-800 for BIF?
Steve Spencer wrote:
I don't think so. There is the grey thing (it is highly blurred but I would guess a tree trunk) in the background on the left for #2 that isn't there for #4. But I would bet they are the same bird from likely the same burst, so obviously very related shots.
Yes, probably within 1/2500 secs. since wing position is almost exactly the same.
Imagemaster wrote
#2 & #4 appear to be the same image.Yes, probably within 1/2500 secs. since wing position is almost exactly the same.
Jul 19, 2026 at 10:30 AM
p.1 #14300 GM with 2X vs 400-800 for BIF?
billsnature wrote:
Let me give all the caveats so I don't get called a moron!!
Shot on different days. Small birds with huge crops. It is a protected breeding area so you can't leave established trails to get closer. I know the "other factors' are likely to be as big as or bigger than the lens differences, but that is why I am asking the question.
Here are 3 from each
Those are really nice shots of Bobolinks. I helped USFWS do a count of Oregon Bobolinks (I didn't know they existed in Central & Eastern Oregon}.
Let me give all the caveats so I don't get called a moron!!
Shot on different days. Small birds with huge crops. It is a protected breeding area so you can't leave established trails to get closer. I know the "other factors' are likely to be as big as or bigger than the lens differences, but that is why I am asking the question.
Here are 3 from each
Those are really nice shots of Bobolinks. I helped USFWS do a count of Oregon Bobolinks (I didn't know they existed in Central & Eastern Oregon}.
Jul 19, 2026 at 04:53 PM
p.1 #15300 GM with 2X vs 400-800 for BIF?
A1ii + 400-800 vs A7RM6 + 300+2xtc
I am sure you can figure out which is which
I am sure you can figure out which is which
Jul 23, 2026 at 06:26 AM
p.1 #16300 GM with 2X vs 400-800 for BIF?
Man, sitting here on my phone I can't tell lol.
Been thinking of getting the 300 lately and selling off my 7RV and 70-200gmii...but not convinced 300 will be long enough for anything I shoot besides some random sports.. Have a 2x as well, could sell the 400-800 too, but 800 is such an awesome focal length. Wish they would come out with an purely 800 F8 G or something.
Been thinking of getting the 300 lately and selling off my 7RV and 70-200gmii...but not convinced 300 will be long enough for anything I shoot besides some random sports.. Have a 2x as well, could sell the 400-800 too, but 800 is such an awesome focal length. Wish they would come out with an purely 800 F8 G or something.
Jul 23, 2026 at 08:05 AM
p.1 #17300 GM with 2X vs 400-800 for BIF?
BigBabyMoses06 wrote:
Man, sitting here on my phone I can't tell lol.
Been thinking of getting the 300 lately and selling off my 7RV and 70-200gmii...but not convinced 300 will be long enough for anything I shoot besides some random sports.. Have a 2x as well, could sell the 400-800 too, but 800 is such an awesome focal length. Wish they would come out with an purely 800 F8 G or something.
Or an 800mm f6.3 like Nikon's.
Man, sitting here on my phone I can't tell lol.
Been thinking of getting the 300 lately and selling off my 7RV and 70-200gmii...but not convinced 300 will be long enough for anything I shoot besides some random sports.. Have a 2x as well, could sell the 400-800 too, but 800 is such an awesome focal length. Wish they would come out with an purely 800 F8 G or something.
Or an 800mm f6.3 like Nikon's.
Jul 23, 2026 at 08:20 AM
p.1 #18300 GM with 2X vs 400-800 for BIF?
Douglas L wrote:
Been thinking of getting the 300 lately and selling off my 7RV and 70-200gmii...but not convinced 300 will be long enough for anything I shoot besides some random sports.. Have a 2x as well, could sell the 400-800 too, but 800 is such an awesome focal length. Wish they would come out with an purely 800 F8 G or something.Or an 800mm f6.3 like Nikon's.
The only issue with the Nikon 800mm f6.3 is the long min focus distance. It's great for hawks and eagles, but not great for smaller birds. I found the Nikon 600mm f6.3 with a 1.4X TC to be more useful, but sold it after getting 300 GM and 400-800.
BigBabyMoses06 wrote
Man, sitting here on my phone I can't tell lol.Been thinking of getting the 300 lately and selling off my 7RV and 70-200gmii...but not convinced 300 will be long enough for anything I shoot besides some random sports.. Have a 2x as well, could sell the 400-800 too, but 800 is such an awesome focal length. Wish they would come out with an purely 800 F8 G or something.
The only issue with the Nikon 800mm f6.3 is the long min focus distance. It's great for hawks and eagles, but not great for smaller birds. I found the Nikon 600mm f6.3 with a 1.4X TC to be more useful, but sold it after getting 300 GM and 400-800.
Jul 24, 2026 at 07:17 PM